Because the mods do their jobs and remove low quality answers.

As it says in our rules:

Answers in this subreddit are expected to be of a level that historians would provide: comprehensive and informative. As such, all answers will be assessed against the standards of Historiography and Historical Method. You should cite or quote sources where possible. A good answer will go further than a simple short sentence. As described here, "good answers aren't good just because they are right – they are good because they explain. In your answers, you should seek not just to be right, but to explain."

Askhistorians is not a subreddit where layman speculation, jokes, puns or bare links to Wikipedia pages are acceptable. When you see a thread full of deleted comments, the vast majority (if not all of them) are the kind of low-effort posts that you would ignore in an Askreddit or any large default thread.

It's very closely watched by the mods to keep it serious and relevant. Keeps the answers on point and no drama.