What do you expect is the reason this happens? I would suspect your skill assessment after a handful of interviews is sound and most people liked you. Do you think you just run into a person eventually that doesn't vibe?
Two months ago a founder reached out to me, gave me a coding project, I completed it (and got paid!), spoke with his co-founder, and then...nothing. At least I got paid but man, YOU reached out to ME. I don't get it.
I wonder if there is some kind of legal liability involved with sharing feedback with potential candidates? I know this is sometimes the case for referrals/what can and cannot be sad in a reference check, etc.