So easy. Social websites are about the community, not the platform. If the people move, so will the discussion follow. Reddit now has no one that's worth talking to. Everyone worthy of having a meaningful discussion with has already left.

Now youtube... that's different... I don't think its possible for them to get replaced. Youtube is about the content created by content creators and I don't see any big youtubers moving to another platform, especially a fediverse one, since there's not gonna be adequete compensation to be worthwhile. I mean, maybe they can crosspost, but I'm not sure if the TOS allows that if you have like a special partnership agreement with youtube. Also, storage is going to be a big problem for a competing platform. Videos are much bigger than text. A text-based platform like Lemmy is going to be much easier to maintain than Peertube with videos taking up potentially terabytes of storage per day when the platform starts growing.