The thread is broadly accurate and I enjoyed it when I saw it yesterday. It's pretty good as far as non-academic analyses of the history of the English language go (ETA: especially for someone who isn't an academic who gives a whole lot of technical detail). That said, it gets some details wrong and is a bit selective in the examples that it gives for the sake of making the story more interesting than it might otherwise be for a non-academic audience.

First a definition. The thread is about exocentric compounds, but it doesn't quite explicitly define what exocentric means. Most compounds in English are endocentric, meaning that some part of the compound identifies what we're talking about. A textbook is a type of book, firewood is a type of wood, moonlight is a type of light, goldfish is a type of fish, etc. Because of how English noun phrases are typically structured, the head (the noun that tells us what the thing is) is generally the second element of the compound. In exocentric compounds, neither of the elements in the compound actually identify what the thing is. Consider the word egghead. If you didn't previously know the word and assumed that it was endocentric, you might think that it is a type of head made out of eggs (or maybe an egg shaped like a head). But an egghead isn't a type of egg or a type of head. It's a person who is intelligent. The meaning of the word has to be sought outside of the parts of the compound.

A major source for the discussion of exocentric compounds in English is Hans Marchand, The Categories and Types of Present-Day English Word Formation (1969). Marchand identifies a few different types of exocentric compounds, including the agent exocentric compounds which he identifies as the pickpocket type. The thread is correct that these tend to have negative connotations, although it is not strictly the case that they always do. They seem to only have negative connotations when used for human agents. Marchand cites a number of names for plants and animals that do not have pejorative senses as well as impersonal agents like breakfast that likewise fit the pattern without being pejorative. Marchand views this as a productive form of word formation and cites examples up through the 19th century, but scholars since Marchand have noted that this type of word formation is primarily occurring in the late medieval/early Modern period and coinages are much, much rarer later. Contrast Marchand with Laurie Bauer much more recently here (in an English pre-print version of a paper that would be published in French).

So far, so good. As long as we limit ourselves to human agents, the thread is accurate in its broad strokes.

What it doesn't really answer is where this comes from, and it gets a detail wrong that is relevant to helping understand the answer. It identifies the period of productivity as being 1550-1700, but I would actually push it quite a bit earlier, starting more around 1350/1400, and this will also help us see where it came from: French. One of the earliest examples of this type of compound in English is cutpurse, first appearing in writing in English in 1362, which you can compare to French words like coupe-bourse with the same meaning appearing a couple of centuries before. This kind of verb-noun compound was and is more common in French than it is in English, to the extent that Bauer refers to these as the Romance type of exocentric English compounds.

So what's the deal with English and French? There are different waves of French influence on English. A first wave of influence begins with the Norman Conquest, where elements of high status Anglo-Norman French gradually filter into English. This is often referred to as table French, as it's where the class distinction of cow, sheep, and swine as the English names for the animals becomes contrasted with the Frenchified beef, mutton, and pork that are served at the table. This phase sets the stage for a lot of French influence, but it takes some time to really filter into English. By the late fourteenth century, there's another wave of influence drawing not on Norman ancestors but Parisian contemporaries, and the literary culture of London was looking more and more to European vernacular models. And then in the Early Modern period, there were huge bursts of French influence as English itself became more and more important as a language of trade and scholarship, and there was tons of borrowing and loan translation happening in quick order. There was a vogue for what were called "inkhorn terms", words that authors would spill from their inkhorns for the sake of seeming intelligent, sometimes without really grasping their origin, which John Skelton parodied in the poem Speke Parott, which has a lovely YouTube performance here. But the English weren't just interested in new high status words. They were also fascinated with what was called cant or thieves' slang, and many of the earliest dictionaries of the 16th and 17th centuries would be hard word dictionaries that encompassed both high status language drawn from French and Latin as well as low-status language of the criminal classes. The roots of these compounds were in the 14th and 15th centuries, but by the 16th century we're looking at a time when the English lexicon is growing by leaps and bounds, and French models are playing an important role here.

So that's what's happening in English and where they came from. But why did they stop being productive? That's a bit harder to answer and requires some informed speculation. But back to the thread. It only briefly touches on the issue of how agents are marked in English, and it does so in kind of a cursory way that I think is a little misleading. It identifies the suffix -a as the agentive suffix in Old English and contrasts it with modern -er, which it says is from German, and -or which is from Latin, but this is actually a little bit garbled. The -er suffix isn't from German; it's from Proto-Germanic, and it already exists in Old English as -ere in words like bæcere, baker, and leornere, learner/disciple. And this isn't the only agentive suffix. Another common agentive suffix is -nd, which uses a participle form of verbs to create agent nouns. Fulk and Hogg, who literally wrote the book on Old English morphology, identify additional agentive suffixes as -icge, -estre, -ele, -ige, -bora. Interestingly, Fulk and Hogg don't identify -a as an agentive suffix, although some other scholars do. Somebody who is a better philologist than I could say more certainly why that is, but I think the issue is that the -a is just marking the noun class, not marking it as an agent specifically, although some number of weak nouns derived from verbs do refer to the agents.

That's a whole lot of technical detail, but the specific point is this. The thread presents how agents are marked as moving away from one system of marking agents to another system, with this appearing as an interesting phenomenon along the way. In reality, it is more like you had a number of different ways of marking agents that already existed in English that narrowed over time to one standard way of marking agents (-er) that was already present in English from the beginning. The French-derived exocentric compound agent was entering into an already crowded field that had already undergone considerable consolidation to -er by the late 14th century that was strengthened even further by the French/Latin -or agentive suffix which served a similar purpose and looked quite similar too. Even in the times when this compound was most productive, it wasn't really anywhere near as productive as other ways of marking agents in English, and it likely isn't too surprising that it would fade as the direct influence on English by French became more a historical artifact than a present reality.

to be continued with a little side-note

(ETA: I originally used cowhand instead of egghead as an example of exocentricity above. However, I think it was confusing people because hand can also refer to just a person who does manual labor. Both egghead and cowhand are exocentric compounds that rely on body-part metonymy for the construction of meaning, but because hand can also be used independently, I can see how people might argue that it is endocentric, so I changed examples for the sake of clarity)

You may want to cross post this in r/linguistics

Hi hello I wrote my Masters Thesis on this very specific type of word. It starts back with the Norman Invasion in 1066 when Norman French becomes the predominant language in England. It's true that a lot of these what I call "cutthroat compounds" were created from 1500-1700, they are still being made up through 2022, even though it's not a very productive pattern. That burst in citations in those years probably comes from the fact that a lot of dictionaries and translations of works (from French and other Romance languages where this pattern is common) were published, and also because Shakespeare (his ancestors were soldiers) probably liked the pattern that his surname had, came up with 15 new ones, and integrated ones into his wordplay which popularized the form around that time. I have collected over 1,450 unique cutthroats from 1050-2022 so far.

Cutthroats are just so fun and childish and evocative that the few (30ish) terms that survive into modern English continue to inspire people to make more. There's also a moment in child language acquisition when English-speaking children spontaneously create these compounds as they are trying to navigate turning phrases we use in running speech into the more common noun-verb-er compounds that we make all the time in English. (he's a fight-fire, he's a fighter-fire, he's a fire-fighter).

So. cutthroats exist because of hundreds of years of French influence, English was receptive because although French is left-headed, our shared VO (verb-object) ordering makes this pattern make sense, we experience this form during language development, and because good insults are memorable, so it doesn't take many of them to keep it going.

They are also used for tools, games, regional plants and animals, adjectives, and many other things, like abstract concepts. Many of the terms for people also apply to objects - like spitfire, which used to be shitfire, which can apply to a fiery person or a cannon or other weapon (like a plane).

I've given quick 5-minute talks about this and lengthy rude 20-minute talks about this. There's a lot to explore about them, and the aim of my research since grad school has been about collecting all potential cutthroats and let someone curate the heck outta them. I find new ones every year.

More about all this on my site: http://www.encyclopediabriannica.com/