I do not think even in this supposed millenial NSA sex paradise we supposedly live in that the average 18 to 22 year old male has bountiful sexual opportunities with the average 18 to 22 year old female.
Statistically speaking, the "younger generation" (than me) has less sexual opportunity than I did. As you said, frequency is down as is distribution. Now, in the group having sex is casual "I'd just like a F" now an effective/good pick up line? I don't know. Seems like it's better than it used to be, Tinder being presented as exhibit A, B and C in that list. However, I've read that there are certainly some (portrayed to be a lot) of women who are upset that their generation has become "Tinderfied". Where, if I was a man of that age, it would be the best thing since sliced bread (actually, a lot better than that, but, hey, that's the saying).
I'm not sure "bountiful" sex has ever really existed for the vast majority of 18-22 year old men. I was pretty good at getting it, and had more than most of my friends, but the effort required nearly consumed my life. Yes, it's doable, but man, you're gonna work for it. And I consider myself a good looking guy who had his act together at that age, had the right friends.. It was still a ton of work.
So when women go out and have their NSA sexual experiences as they are encouraged to in today's world, they likely have them with a subset of the available men.
Men, in general, live at the extremes. The smartest people to have lived were almost all men, the dumbest were too. The richest people in society are almost all men, the poorest living in the streets, almost all men. Men "deviate from the norm" much more strongly than women, some men sleep with 1000 women, some struggle to find one. The rewards are huge, but the pitfalls are also huge.
I think this applies to affairs too. My W has had one affair. Her AP has had several (discovered by his W, lord knows how many others). The men I know who cheat, with one exception, aren't "one and done", they cycle few at least a few, and some of them a lot of APs. Yes, the cheating rate between the sexes is similar, but, I'd bet my life that if you looked at the number of AP's per male vs female cheat, the number would be vastly different. Again, living a few standard deviations from the norm.
Whereas any particular man going through the same times is just obsessed with his particular fetish
I'd put it this way, speaking for myself. I wanted sex because I wanted sex. Not validation, not a girlfriend, not a wife, not someone to listen to me talk, not a new friend. Nope, I wanted sex because that's what I wanted. Not really a fetish, but the desire was aligned with the actions that I took. I wasn't trying to "fit in", or be the "big man on campus", quite the contrary, I'd sleep with women and lie about it to everyone "Nahh, she blew me off" to protect her reputation (which, selfishly, was good for sleeping with the woman again, too many guys bragged and made their hook ups look bad).