The big thing was the creation of FaceBook. People shut down their websites and forums, and moved everything to FaceBook. Initially, FaceBook gave a ton of traffic to people who did this. Then, once they had a monopoly, they said "If you want to reach your followers, buy ads." All the people who shut down their websites were screwed, but there was no going back.

It's much easier to post on Reddit/Facebook/Discord/etc., than trying to create your own website or your own forum.

You can make your own website, but Google now maintains a "preferred website" list for search rankings and also "banned websites". If your site has anything controversial, you wind up on the banlist.