I read somewhere on here that Kbin doesn't have an API available right now and that Artemis is making their own API through scraping. That'd play a big role if it's true. I also wouldn't be surprised if migration numbers were skewed towards Lemmy either.
Boost confirms switching to being a fediverse app after the Reddit app shutdown. (www.reddit.com)
Right now it's going to be for Lemmy, but the fediverse is still getting a fantastic app.