Yes, the fediverse exists, but I would think the majority of non tech nerds leaving twitter would either leave social media entirely or move to another corporatised platform. Killing twitter is a net loss.

Also, how is Youtube not a social media platform? It has community posts, shorts, long form video and comments on those videos, all where people interact with each other. I'd even say it's probably the biggest social media, people spend a lot of time on it.

Sure, facebook is trying to join the fediverse with (the currently failing) Threads, but anything on their server is in their control, and the fediverse isn't doing anything to protect Threads users. Migrating from Threads will also give the users a subpar experience (because of the lacking integration into Facebook's services) and make them feel like the fediverse is just a worse less polished platform.

Maybe DIGI does have a commitment to something, but I personally cannot trust Facebook and Google at all to enforce it fairly.