It's a striking vs grappling thing mainly. Some guys (mainly grapplers) refuse to tap to submissions too.
The general idea of tapping to strikes being a bad thing is that it suggests you're a quitter. You're conceding before you're actually finished. Think of the old phrase "over my dead body" - you're not supposed to stop fighting until you literally cannot. In my day, tapping to strikes was considered quitting, a bitch move, being a pussy, and all that. Big no no. It's like that still in most strike-heavy gyms, I'm sure, but probably a little more lenient than it was with all the "brain damage" shit being pushed by white knight fanbois lately.