Mastodon is never going to be That Platform and that's ok. It doesn't need to be. The ActivityPub protocol is the highest value aspect of Masto, and there are a handful of other, larger, easier to use platforms that are adopting it.
I'm not sure if people looking for something laid out like Twitter or other microblogging sites would necessarily move to Lemmy, which is more like a forum. The activities on any social media may be largely the same, but presentation matters a lot.
To me, Lemmy and other forum style SM is like going to a bar and finding people to have a conversation, where as Twitter/BlueSky/Mastodon/etc are like standing on a street corner and just yelling random thoughts.
Threads is implementing it in phased rollouts and I think they saw the writing on the wall with X that Bluesky was the next "big thing" and wanted to jump on a competitor protocol that had already been developed and already had an active base of both users and developers.l, whereas Bluesky is building everything in house from the ground up with the AT protocol.
WordPress has a plugin that is developed by Automattic (as close to core WP as you can without actually being core WP) which essentially turns every WordPress site into an ActivityPub feed. Its really cool and an incredibly powerful tool for publishers.
Flipboard is also implementing ActivityPub as we speak, and it seems like they are quite bought in on the concept. Their CEO hosts a podcast about the Fediverse.
Ghost is a publishing platform similar to Substack that is also working to implement ActivityPub and is doing a lot of the heavy work in terms of trying to figure out what longer-form publishing could look like within the fediverse, as opposed to being a network of different Twitter clones.