Strictly speaking from a purely biological perspective, a woman does not have to cum. Mindset, attitude, particular attraction, etcetera all go into ensuring that people don't just bump nasties willy nilly with it being mutual pleasurable and women get the short end of the stick.
It's not "as sensitive as a penis". There's a great deal more nerve endings, but none of that matters if the other switches aren't flipped and even then, part of it is mindset.
In terms of complexity there's a great case of the "female Viagra" drug which was basically a barbituate designed to work like alcohol that didn't even work. Name escapes me at the moment, maybe someone remembers it.