Well, if you have to ask, then there's not much of s point in any guy answering, because it's either going to go in one ear and out the other, or your inner child is going to pull out its sword and shield and try to vigorously defend itself.
Guys want to feel sexually wanted. Guys want to feel desired, not faintly (meh), but strongly and passionately. Guys want to feel hungered for, they want to see and feel the lust their partner has for him.
"Good girls" don't give that feeling to a guy. Instead, they make him feel like, "Okay, we can have sex my love, if that's what you want to do. I love you, so I will have sex with you. Yes, I enjoy our pleasant moments together, and I enjoy pleasing you." O. o A guy looks at that and thinks, "She doesn't really desire and want me 'sexually,' and if we continue down this road, sex will one day become a chore for her, and I'll be one of those guys that has no sex life."
"Sex," for "good girls" is a symbol and source of narcissistic identification. Their sense of personal identity is linked to how "easily" they "give/have" sex, and how "difficult/hard-to-get" they are, because the more difficult and less easy they are, the more worth it they must be (hence, narcissistic identification, by definition). That's why you often hear "good girls" saying that "sex is more emotional" for girls.
In contrast, the "slut" or "slutty" girls, simply lack the same craving for narcissistic identification through sex. As a result, they either have no interest in sex, or their high sex drive is more freely expressed through action.
You have to remember, guys don't do subtle. Guys only understand overt, blatant, explicit, obvious. So, the slut makes him feel ways he's longed to feel his whole life, and yet remained unsatisfied in the hands of other women. the slut makes him feel like, "I want sex. I want you. I enjoy how you make me feel. I enjoy you inside me. I enjoy feeling free and wild with you. I enjoy you wanting me. I enjoy making you want me, and then feeling you inside me fucking me hard. I enjoy all of that because you satisfy me. And so, I'm angry and upset when I don't get to enjoy all that with you." O. o A guy hears, "She wants sex for her. Not likely to be a sexually miserable relationship. Not likely to play games with sex and 'withhold' sex, because her penalty for not having sex is just as high, if not higher, than mine."
So, guys prefer the emotional comfort and security of slutty girls.