came up with things like decentralization and activity pub which are unlike any of the big platforms of yore.

I personally think activity pub is overrated. Not that it's bad or anything. But many think of it, IMO, as the beginning and end of a new form of social media and people taking back the internet. In reality, I think it's literally just a protocol and so much more than people recognise depends on what people build on top of it. So far, for example, the limited interoperability between lemmy/kbin and the microblogs/mastodon, which is not a simple bug fix away, at all, is a major friction between these two platforms that essentially forces them to be separate spaces/platforms. This is so despite both using ActivityPub and actually federating with each rather well. Because, it's not (just) about the protocol, it's about platform designs and structures ... IE the software ... and the protocol can only do or guarantee very little on that front.

From what I've gathered, the diaspora people didn't adopt activitypub in large reason because of this, and I think they've always had a point. The pain some users have gone through trying to work out how to use lemmy and mastodon together, having been promised that ActivityPub is a whole new thing that creates a deep and wide fediverse, has been awful to see.