For me, it is because Mastodon (the Fediverse generally) doesn't actually solve the problem of decentralizing social media. It is reasonably decentralized in itself, because it is federated, although that is problematic because it gives too much power to geeks who can figure out how to run ActivityPub servers (which isn't easy). There are other technical issues, too; for one thing, I understand that a key pair identity system is misused, making no use of private keys, which enables server admins to forge posts by participants.

But the most important thing is that no single network is going to replace Big Tech social media networks. Basically, there are too many competitors. They need to be made interoperable. And as far as I can tell, the single biggest impediment to interoperability is (a) the lack of a social media data standard, that (b) is commonly used by a lot of people with social media content to share, in which (c) people actually own and control their own data.

The biggest way to fix that problem is to create a "lingua franca" for social media—not just a standard, but a tool, or an app, that is really easy to install, which makes it possible to manage all your social media from the same place, and you 100% control it yourself. So that's why I'm chasing down a plugin for WordPress. It's easy to install WordPress & WP plugins. Then we just create importers and exporters to and from RSS (a slightly extended version, perhaps).