Because men tend to fall into two categories:
The Bad Boy - the man who will take you out, boss you around a bit, stick up for you, get angry at someone who hurts you and just generally make you feel like a woman.
OR
The Nice Guy - the boy the buys you dinner, agrees with everything you say & tells you you're the love of his life by the second date.
Im sure there are some lovely gentlemen who fulfill both these HUGE generalisations, but in all honesty they are few & far between.
From my side of the fence - I want a challenge, someone who can stimulate and excite me or show me something new and if they're just a little bit of an asshole with an abrasive manner, as much as i despair this quality, i can put up with that. I cannot put up with someone who bores me stupid but is nice as pie, id rather be mates with them than pursue any sort of intimacy.