I think a bigger reason than any of those is that the web became a corporate advertising tool, run by bean counters and marketing people who don't like "weird" content because it may scare some people away. Just like TV, web content now targets the lowest common denominator and anything confrontational or "weird" gets put on niche sites or self hosting out of the limelight.
I think there are still a ton of "fun and weird" sites out there, they're just not on highly promoted, corporate backed platforms. And they're now a much smaller percentage of the entire web.
Actually, they're not that much scared that weird content will scare people off, they just don't like weird content exactly because it's weird and therefore unpredictable and hard to put into Excel planning charts.
The end result is still things like “wow, my tumblr account sure is a lot quiet now that all the people I was following because I liked their weird cartoon porn are gone”.
No, FOSTA hit sex workers. Tumblr just decided that lewd stuff would make it hard for Verizon to sell ads, so they banned lewd stuff and anything their shitty algorithm thought was lewd-adjacent. Now they're down something like a quarter of their former userbase, depending on whose estimates you believe; it might be higher. So that'll really help them sell those ads!
I think there are still a ton of "fun and weird" sites out there, they're just not on highly promoted, corporate backed platforms. And they're now a much smaller percentage of the entire web.