Being a jerk is a negative emotion. Women avoid negative emotions like the plague. Being a jerk == the nasty nerd
Being "too nice" and being a jerk are both types of insecurity. They are afraid to just truly be themselves and just "be", so they try to compensate by acting aloof, trying hard to act cool or like they don't care, becoming dismissive or never asking a woman out to protect their fragile male egos from rejection.
This stuff repulses women as they know an insecure, needy man like a guy can spot a 500lbs fat chick with warts.