There is no woman who doesnt enjoy giving blowjobs. If you cant teach her right, it's your fault, period. Maybe they had bad experiences with previous exes but it doesnt mean they cant enjoy it if they learn it the right way afterwards. It's up to you to create the adequates circumstances anyways, it takes time and patience. A good blow job requires both female AND male to feel relaxed. We are all ok for sex when we re stressless, happy with most things in our lives.
Think about it. Does it really make sense to wash your hands *after* you go? Did you pee all over them? No! Your hands were filthy BEFORE you went. Then you wrapped them around your *getbig sized* pee-pee 
All you guys who think you're clean 'down there' HA!
oh come on. It all depends of many factors, degree of horniness on the moment etc, it's entireyl situational, a woman can crave for cock even if a man isnt shaved/clean etc if she s on her periods or if she has something to be excused for -having been a bitch during the day and being shameful of it-. But because it happens -she getting exceptionnaly horny to the point of wanting to gag on your cock- once doesnt mean she s going to always do it that way... that's what makes these moments so enjoyable.
And both men and women work exactly the same -we feel things the same way, except genitals are extern for males and internal for women- the difficult part is being "on" both at the same time. One thing is sure, women often think they are bad suckers, basically they dont know if they give the man pelasure, and it becomes a chore. They underestimate their skills and as a result "dont like it".
It takes time for a girl/woman (virgin) to learn how to do it right, but as for everything in life with work you get results.
Obviously being genuinely in love with the person helps alot.
