I don't know, on the other hand, "random" is kind of a tired aesthetic.
Little inspires less confidence about someone's creativity than schizophrenic jumbles of gifs.
Besides, there wasn't a reduction in fun and eccentricity. So lets permit for a second that being "random" and being fun and eccentric are the same thing (they're not). Part of fun and eccentric moved to video games, the real safe space on the Internet for it. Part of it went away because personal websites became public facing destinations in a way MySpace and Geocities pages never really were.
And before you say that MySpace was a public facing destination, it is proving my point that musicians rapidly moved away from it long before Spotify homogenized the way we access music - it wasn't a music industry thing. It's that Instagram does a better job at doing what MySpace did, and it's because non-random people just communicate with pictures of themselves, particularly their bodies, as the lowest common denominator.
Why is the loss of "wild creativity" no real great loss? Ultimately we can appreciate how hard it is to design nice looking stuff a lot more. Even nostalgia for that old Internet you're talking about is kind of toxic, especially to people who are genuinely random, because nostalgia is a huge obstacle to getting people to try new things. And that's why maybe those blocky design frameworks are here to stay - because stuff that feels visually familiar on something that doesn't really matter, like a website, convinces the visitor to try something new that does matter - whatever you're writing, composing, making, etc. that you're putting on the web in the first place.