I was impacted by the closing of mastodon.lol and I never recovered either my follow count, or frankly my interest and engagement in the platform since. I'm not alone, either. The 'migration' behavior was half baked at best, giving me what equates to a 301, not much else. There's a lot of work to be done here.
I am the most active on Threads for my brand account, and my personal account on Mastodon is a distant second. I know the people here are gonna throw shoes at me, but my activity is on Threads because that's clearly where the numbers are for my field and the market outside of the total loss that is Xitter.
Mastodon is probably not going to be any bigger than it is now. But you can self host and dictate your fate. In a time of protocols, not products, existing is a great place to be in. Make your own fate.