I don’t think anyone suggested Meta is doing this out of the goodness of their hearts. I certainly didn’t write that. They want to make money.

As for cross-pollination, it’s basically a law in SaaS now. When you expose users to something, some of them engage. Meta can’t hide the existence of other instances else there’s no point in federating. If users are other instances, and interact with users from those instances, some of them will create accounts on those instances.