Because one ultimately embraces what it is, and one does not. And I mean that both for the characters themselves, AND their respective stories.
Robocop had some serious bullshit happen to him, had his life ruined, and in the end managed to put his big boy pants on and get over it. He can't go back to being "Alex J. Murphy", but he doesn't have to be just "Robocop" the corporate puppet. He put the two together and moved on. You never see robocop crying about how he hates what he is, or harboring some grudge against OCP. He just says "fuck it, I'm armor plated, have an auto-9, and get to maul crackheads on the daily, I'll have to make due". Yeah, he's hurting on the inside, but arn't we all? He keeps that shit in, and focuses on the good things in his life, like the a fore-mentioned beating the shit out of scumbags.
And robocop's world is his own. there's nothing else like him. He gets to look every bit the powerful super-cyborg, because there's no spandex-clad geeks flying through the air shooting laser beams out their eyes or shit. ED-209's a dumb robot, Cain was a monster, and we just don't talk about the robo-ninjas from 3. There's nothing "Better" to compare him too, he is THE Robocop.
Cyborg is a whiny bitch. His entire character is "whoa is me, I hate myself and my daddy, I don't fit in because reasons, and am a emotional shit". Like most comicshit, cyborg has this "my gift is my curse" Greek tragedy shit. If Cyborg got his shit together after, say, throwing a bus through some giant radioactive bug, while shooting laser beams and shit and went "Hey, this may not be what I wanted, but there's fags out there who can't even open a jar of pickles, maybe I can make this work, maybe I can be something newer, better", then I'd like the guy.
Also, cyborg's world is not his own, he's just another super-powered guy in a UNIVERSE full of super-powered guys. He's unremarkable.
Robo kicks ass, Cyborg cries.
https://www.youtube.com/watch?v=c-eZeVwnVOo 
