It's a chicken and egg problem for sure, but what I find a bit funny in every case like this (Reddit -> Lemmy, Twitter -> Mastodon, etc) is when someone says "X doesn't have any users!" it makes me want to reply with something like:
Well of course, if X had anywhere near the population amount of [Reddit, Twitter, Etc] then its likely that these changes wouldn't be happening in the first place, to avoid a migration...
These companies think they (and unfortunately in a lot of cases, are) too big to fail, if there was a competitor out there that had another sizable slice of the pie, then I doubt they'd be making idiotic changes like this nonsense over the API.
I know that this is just how the network effect works, but it does make me laugh for a moment every once in a while.