I would add that women also don't understand it because they don't operate visually as men do (with respect to sexual images).
Now, I'm not sure that's the best way to put it but the fact is that there is only a fraction of porn for women vs. porn for men. No market apparently?
If there was an innate need in women for porn and sexual images there would be a market created for it and there would be much more porn targeted to the female market.
Back in the day there was pretty much only 1 printed magazine with images of naked men "Play Girl". And some would argue that that was actually read quite a bit by gay men as opposed to women. But there were dozens of magazines which a man could buy. On a newstand at least.
If women were stimulated the same way as men someone would have exploited that, right? But they didn't.
Same with the internet. (Wouldn't want to guess at the ratio if anyone knows please post.)