If you zoom out to a few years you can see the same pattern over and over at different scales — big exodus event from Twitter followed by flattening out at level that is lower than the spike but higher than the steady state before the spike. At this point it would make sense to say this is just how Bluesky grows.
Besides that, the entire point of this project is to increase the barrier to entry for potential contributors (while ideally giving good new people a way in). So I really don’t think they’re worried about this problem.