Beer podcaster, judge and occasional historian here!

So, for the first question, there are a few answers to unpack. You're absolutely correct about the influence of Anchor's Fritz Maytag as 'setting the tone' for much of what was to come, although Anchor Steam specifically would not be a 'British' beer style, but much of their other output, especially early on, would fall broadly into those categories. Another big early influence was Bert Grant, with his (nominally) Scottish Ale, though he also brought out an IPA much earlier than many - more on that in a moment. Beer writers like Roger Protz and Michael Jackson championed both Maytag and Grant in the early 1980s. As what might be called the first generation of what were then called 'microbreweries' opened up (before crashing in the early 1990s - another story entirely), they tended to follow this broadly 'British' template. 'Microbrewed' beer quickly became stouts, porters and bitters, though, of course, with local variations - a look at Manhattan Brewing Company from 1984 gives a good sense of the typical lineup.

There's more complexity with the 'why not German styles?' part of the question that I'll try to summarize, but I highly recommend checking out Brian Alberts for top-notch historical work on German and German-American brewing and its wider role in society. First, German-American brewers were, with some obvious exceptions, hugely impacted by Prohibition - their growing political influence in the late 19th and early 20th centuries - or, more accurately, the fear of their 'foreign' ways - was a key element leading to Prohibition, and few recovered. Those that survived Prohibition would become the familiar macro-lager producers that the eventual craft beer movement was 'against' - the beers they produced after the second world war were (mostly) the 'lawnmower beers' early craft beer brewers railed against. Maureen Ogle's Ambitious Brew is a great read on this topic - there is much more to explore.

There's another technical element, though - lagers are, quite simply, harder to make well than ales (this is a *very* broad generalization), requiring more precise temperature control and, depending on how they are served (e.g. on draft immediately, canned, etc) may take up more time in tanks than a small brewery can spare, even today. A brief aside - one reason so many German brewers moved to the US midwest was the availability of caves that gave them ample space to lager their beer - for those who don't homebrew, essentially a cool place to store them until they were ready to sell.

So, you have a combination of British (or, perhaps more accurately, British-inspired) styles setting the template for what craft beer 'looked like' early on, plus an anti-lager 'backlash' as lagers were often perceived as flavorless or bland - this attitude still persists to a certain extent in less-mature craft beer markets, where 'lagers are bad' is still thrown around on places like, er, Reddit from time to time - and if you are operating on very thin margins, it may simply make more economic sense to make ales for a variety of reasons. That said, there have always been regional exceptions, with lagers being at the forefront of other craft beer scenes in the US, especially from the late 1990s-early 2000s on - PA's Victory Brewing is a good example.

And as to IPAs - this is an interesting one. While the aforementioned Bert Grant made one in the Pacific Northwest in the 1980s, it's hard to recall now that the style did not really catch on until the very late 2000s. Back in 1994, the British Guild of Beer Writers held a conference dedicated to IPAs, with Brooklyn Brewery's Garrett Oliver bringing their East India IPA, but even in the early-to-mid 2000s, there were relatively few of them available commercially, and then, they explode as a category, first in the US, and then elsewhere.

Bitters were actually very common in US craft brew prior to the IPA 'explosion' and there are a few milds (again, regionally - there are excellent examples in Philadelphia and Seattle), but it can seem, nowadays, that it's simply a sea of IPAs (many of which would not have been recognized as such 10 years ago, but hey, styles evolve). There's a broader conversation to be had around 'is everything an IPA now?' that's happening in the beer community, but it will take a while before we have the distance to look at it historically; it's still happening right now.

And there are more German styles (or, again, perhaps 'inspired' styles) like gose and Berliner Weisse being made by craft breweries around the world nowadays, though these once-regional/historical styles don't always bear much resemblance to their modern counterparts, nor, sometimes, even to versions made just a few years ago.

After being very long-winded there, and any errors/overstatements are my own - apologies - it's probably fair to say that the Oxford Companion to Beer is due for an update or two...