Why don't women ever go for nice guys ?

are you sure you are really a "nice" guy?
'cause you just called a stranger a "slut", so you aren't really coming off as "nice" here.
it's actually scary, 'cause you went from "nice" to "angry" in the space of one comment.
if you behave like that IRL, many women probably find you impulsive and threatening.

but... if you think all the girls you are interested in are "sluts" why aren't YOU going after a "nice girl" instead of aiming at "hot chicks with bad judgement"?

would you "do" a girl you weren't interested in to "save her life"?
or would you just think "what are you talking about!? i don't owe you anything?!"

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but her answer wasn't shocking. It was a guess as to why you might be having this experience. As we don't really know you, we have to guess based on our own experiences with people who have a similar mindset.

and you say it "just came out", meaning it's hard for you to restrict your impulses. Again, this will scare many women.

This is not true. And if you think it is, you're going after the wrong women. Either they have mental problems and are attracted to jerks, or simply can't allow themselves to get close to a guy(which may be why they go for jerks, because they know they'll get pushed away), or they're just not attracted to you. And if they're not attracted to you, it doesn't mean you're unattractive. It just means you're unattractive to one girl. And you can find another girl who thinks differently.
If you find yourself hopelessly attracted to girls who go for jerks, impossible situations and unavailable(meaning unavailable to YOU, not just single and not dating anyone right now) women, you need to do some soul searching to figure out why this is. You know there have been girls that have been attracted to you in the past. But for some reason, you passed these girls up. Why?
I think many eternally single nice guys are kind of romantic fantasy addicts. They used fantasy as a coping mechanism at an early age. And they have difficulty breaking out of it later in life. What they really want is intimacy with a female. Where they always end up, and where they're comfortable, is in wishing, hoping and dreaming about some out of reach girl or impossible situation. To recover, they need to work on breaking out of the cycle, to get more comfortable in reality.

No best answer !!!

They're not exciting like bad boys.

We do. I am dating a very nice guy. We don't go for the self-proclaimed "nice guys" though, because they are hypocritical and not very nice at all. If you think "being nice" is all it takes and then get mad when women don't feel a connection to you then you're actually not nice at all.