I feel like part of the problem, speaking as someone who plays characters who are capable but not perfect, and tries to protray them like that, is that a lot of the time if you're anything less than perfect you get treated like an idiot by the characters. So people who play even capable but not perfect, or even relatively normal but not a total idiot, types of characters end up feeling like they have to be always on point if they don't want their character treated like a dunce by everyone else. It's like any mistake, no matter how understandable, is liable to get you treated like you're too dumb to live.