In society, women are not encouraged to experience pleasure in the same way as men. Men and women are conditioned to view sex and pleasure in
completely different ways.
To give you an example: I didn't understand where the clit was until high school sex ed. Before then, I thought all the ~good feeling parts~ surely must be inside
If I didn't put that together until my teens, imagine how many dudes didn't get how important clitoral stimulation can be?!
While plenty of men figured out how to jack themselves off from a young age, many women were in a similar position as I was and didn't figure out what felt good until much later.
Could that make having an orgasm a bit more difficult? You bet.
Also, consider what we see in porn. It effects how we think sex is supposed to go. We've all seen someone getting jack hammered by a dick before in porn, right? Doesn't necessarily feel great, but because we've seen it so often, we assume that's how it's supposed to go. Then there's the assumption/expectation that all sex
should include orgasms and was terrible if it didn't. That's not always the case.
Another important factor to consider here: when you say sex, are you only referring to heterosexual penetration?
Cause I'm sure if we explored the statistics in lesbian relationships...the numbers in that statistic may different