Just how Twitter, YouTube, fedi, etc. can’t take your follows or followers with you outside of each respective universe. Each implementation of a social graph is closed in and not transportable. I’m Not super familiar with fedi, my guess is you can transport those things between fedi servers but it requires effort and maybe cooperation?

But the pain of starting anew makes the users “sticky” less likely to move. Nostr social graph is easily portable between relays, though the whole thing is experimental. But still it’s not like I can bring all my follows with me to fedi or Twitter or YouTube either.