On the other hand, I think the Reddit migration has a lot better chance of succeeding than any attempts at Twitter or YouTube or Twitch migration.
On the three other sites I mentioned, you’re following specific people. If those people don’t make the jump to a new platform, there’s little reason for you to make the jump either - you’re not going to see the content you want on the new site. Reddit and kbin and lemmy, on the other hand, are community based. I can talk about movies and woodworking and programming memes here just as well as I can on Reddit. The content is the discussion, and anywhere you can find groups of like-minded people, you’ll get that content.
Other people have mentioned the monetization angle for content creators, which is another factor that doesn’t apply to community-based sites. Hell, a large part of the complaints against Reddit is that they are relying on free content and free moderation. So that barrier isn’t holding people back here.
Last point, at least for YouTube and Twitch, is that video hosting and streaming is expensive - any competitor, if they want to gain serious traction, is going to need a lot of money behind it.
From the Apollo side :(