I agree actually, when I was joining Lemmy a few days ago I looked at a few instances and they all asked me to write a blurb why I wanted to join that instance. I get it and I think that's a good way of curating a community but I wanted to switch to Lemmy right then, not in a few days when my application is reviewed.
I ended up on sh.itjust.works which didn't ask for any of that and just gave me an account, but I think quite a few people like me won't want to wait until their application is approved.
Trust in admin(s).
You're trusting the person running your instance to do a good job, to provide good hardware and keep it running, to ensure it isn't de-federated from other instances, to provide Lemmy software updates, to not ban you or vanish one day.
Really, I don't know who my admins are, I've read a few posts and they seem pretty good, but I've not seen them before. But really, this is what it will come down to in the long run.