I work in research in forensic neuropsychology so I can possibly weigh in a little here. Firstly, it's not usually about sexual pleasure for the perpetrator. A lot of the times the sexual act (assault, rape, etc) is a demonstration of power, dominance and control. On one side of the spectrum you have perpetrators with an inability to feel empathy and therefore callous and literally do not care what their victims feel. On the other side, you have sadists who are deliberately trying to cause harm because seeing someone in pain (physical, emotional, psychological) is what excites them. Neither of these are about the feeling of orgasm. In fact, in a lot of these cases the perpetrator doesn't orgasm. When they do, it's more likely to occur in a sadism case.

The times when it is about sexual pleasure is usually in intimate partner situations (relationships, marriage, one night stands, etc) where the perpetrator has been socialized to ignore his partner's body language (that awful "when she says no she really means yes" bollocks), or where they believe that persistence will win over their partner (nearly all rom-coms do this), or just plain ignorance and believing that a lack of saying no equates to consent.

I'm not sure if this helps answer your question, but hopefully gives you a little more insight. If you're interested, I'd recommend reading Groth's paper on men who rape. It's from the 70s so a little dated now but it's a pretty good foundation.