An orgasm comprises of two parts --- the mental aspect and the physical aspect.
Just from listening to others and surfing the internet (yay... such very good sources!)... it would seem that the main hinderance for women would be that the mental aspect is not satisfied. Some women are with men they don't fully trust, they're worried about their performance (yeah, that's right... women do worry about their bedroom abilities as well), or there was some trauma that interferes with sex directly or prevents women from feeling intimate with someone or both.
Very rarely is a woman's ability to orgasm compromised by a purely physical basis. Sometimes, these physical difficulties (given they aren't too severe) can be overcome with the proper mental/emotional stimulations.
For women... sex is more mental and emotional than physical. Albeit, yes the physical part has to be there... but the mental and emotional aspects can be and often are... just as important.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen