What always helped centralized social was an environment of rapid growth. For the majority of people there wasn’t a “before” to compare to whatever they signed up to, so a play like the one Reddit made, which isn’t about the quality of the content but “whatever gets people in the door”, worked - focusing all your energy on hypergrowth was the Web 2.0 strategy. But my own “before” goes back to browsing Usenet over a dial-up shell account(terminal access only). The technology used then was primarily characterized by being efficient to store and process, which led to a federated model that shared text threads.

The reason people switched from Usenet to early web forums was also a combination of not having a “before”, plus some new conveniences. Usenet moderation tools were very limited, ensuring that spam and derangement were common. Because the design was made just for text, you didn’t have image-focused content, but you also didn’t experience the things images get moderated for now - you could post a UU-encoded file that contained an image, or a link to an image, but you couldn’t shove it in people’s face. And tree quoting replies was normalized, if rather disorganized - long-running threads often got “forked”.

The model of web forums that became most popular - flat topic threads, more images, centralized moderation - caused as many issues as it solved. Flat threading with no post ranking makes people reply “first” at the top of the thread, images create a whole attack surface, and centralized mods have more power to trip on. But they could provide a better experience along the narrow set of things they wanted the forum to be about, and that made all the difference. That’s how the centralized model works. When I think of places like Something Awful or Newgrounds in their original heyday - it’s really gatekeepy stuff. There were tastemakers and you followed their lead or else.

Reddit started with a lot of link aggregation, which was also Digg’s thing - that model “pushes” more content than a regular forum, so it helps build broad-audience engagement. But Reddit added more Usenet-like elements, and those gradually took over a lot of the niches as more people started using Reddit to ask questions and make statements addressing a specific community.

Something that I think defines the federated space is that there is less “push”. The power is more distributed, fewer gates to keep. Reddit represented those values for a while, and now it obviously doesn’t, so the users who were there for that are going to drift this way very quickly.