"But maybe I'm just a misogynistic asshole and there are other reasons I can't fathom."
The instant availability of porn is a big culprit. Some younger men are lazy. Some are shy. Some are not attractive in some ways. Some are very busy.
In the old days (i.e. when I was 18-24) you had to get over all this because you had very few options if you wanted to get your rocks off while seeing a naked woman. You had to find an actual female for that.
The other alternatives were not good. To buy a dirty magazine you had to go to a convenience store and try not to feel embarrassed while the clerk stared you down from behind the counter. Dirty movies were usually only shown in cinemas in bad parts of the city.
So, you're 21, you're horny and you don't want to jerk off in the dark using your imagination. What to do? Hey! How about bedding one of the girls on my college campus?! Actual women! What a great idea!
Online porn took away this incentive because it offers instant gratification/relief for younger guys. Who feels like going on the hunt for women after you've just ejaculated over and over to the porn-star-of-the-moment (or old '70s porn, etc.)?
I should also throw in one other thing I don't think guys under age 30 know. Masturbation was a depressing activity before online porn. It was like an admission of failure and felt creepy because you felt so alone.
Because of the solitude factor, you had no "connection" to the outside world. Having porn images on your computer screen creates surrogate humans -- in much the same way having online friends creates surrogate friends. In this sense, you feel a "connection" to women with online porn like you do with friends on Facebook or even this forum.
Granted those connections might be totally fictional or very small, but they're still there. As such, the difference between online porn and jerking off alone (or even to a magazine) is similar to the difference between me writing this to all of you or writing it in a notepad on a desk. That's a big difference, psychologically speaking.
Then there's the ripple effects.
Porn has changed the culture (understatement of the century). We're now a porn-saturated society. The mere presence of porn endorses masturbation which has made it accepted. That sure as hell wasn't the case before.
Decades ago, there was a good amount of shame and feelings of failure if you jerked off too much (or at all). You felt like a loser. Having a girl on your arm was a signal to tell your peer group "Look at me! I'm boning THIS! No masturbation in these parts!"
Now even writing about this feels like I'm unearthing ancient history. I can also find almost any old song I like on YouTube. So what's the incentive to buy music?
Hypergamy plays some role in what's happening on those charts. But to discount such a major cultural shift as porn is to ignore the elephant in the room.
Someday, when they build a time machine and I can take you all back to the '80s, then you'll understand.