I'm going to inject some cynicism and say that what a number of them find unsettling is how famous they
aren't.
They always think they have a big idea. It's never some minor correction to a big theory, which a PhD would be happy with (as long as it's major enough to be publishable); no, it's Shatter The Foundations or nothing. Therefore, they're being done out of their fame and fortune by some grand conspiracy, which, in itself, proves how important they are: If they weren't right, They wouldn't be conspiring against them, now, would they? That mindset certainly sells books, and helps on the lecture circuit, too.
I'm sure there are some honest crackpots, but I wonder how honest you can be when you come upon a bit of well-accepted physics you can't understand or simply don't like, and conclude that everyone else is wrong, and you're the only one who's correct.