I really like that about him, that he's not a mastermind, that there's something fundamentally banal about him, an evil without purpose or ambition beyond its own satisfaction.
Upon reflection, I think that might be why he works so well as an enemy of Diana's. He's a grown up version of the kid who tortures animals. He doesn't do it because he feels compelled, or to lash out at something, but because it vaguely amuses him. That kind of casual cruelty is one of the greatest social ills that Diana is trying to cure, and Psycho is its personification.