These centralized sites makes it easier to stick around.

That forum I signed up for in 2012? I don’t remember the name.

That Facebook group I joined in 2012? I still see the occasional post in the feed.

Also it’s vastly easier to find these communities in the first place. There’s no way to look for forums about a specific topic, if that exists at all.

> From a users perspective having one account for reddit which replaces x accounts for specialized forums makes things easier such as managing notifications, etc.

Forum platforms could offer the same feature by interoperating with the Fediverse. You can sign up on one server and use that one identity to post content elsewhere. (Plus it also addresses the issue of needing a mobile native UX, there's plenty of apps that can interact with the Fediverse.)

Notifications are just one aspect. As mentioned by others discoverability is another. An independent forum has to compete with commercial sites and well the entire www regarding search engine placement to be found.

That said, a lot of communities seem to be migrating to Discord as well, which has a discoverability many times worse than forums, as Discord 'servers' are not even publicly accessible.

Could, yes, but that's besides the point of WHY this has happened

Because the Fediverse is quite new and forums haven't gotten around to adopting it, even though they would naturally benefit from this tech.

Also I would not underestimate the power of push notifications. Forums don't come with their own app and notifications out of the box.