The "nice guy" is often not a confident guy.
Women will respond to self-confidence, but often they confuse the "I don't care about you, I can get another woman" vibe that a jerk projects with self-confidence.
One can be a good, honest person, while at the same time be self-confident enough to not compromise one's essential self for the sake of a pretty woman. The world is FULL of pretty women, once a man realizes that and isn't so afraid of loosing a "special" one, then they will settle down into their more self-confident, "real" self.
Self confidence also allows relationships to shake out as they should, without excessive whining and crying when things are not meant to be.
I am a "nice guy", I'm honest, caring, emotionally mature, and consistent. I also know exactly what I want, and if someone isn't it, she can change or she can go on her way (without malice on my part). This has often made me very attractive, even though I'm physically plain. Now...add to that self-confidence the little "dark" slice to my sexual habits...
I haven't had trouble finding companionship for decades, and haven't had to compromise the "nice" parts of me to do it.
-SB