It's a mix of things:
Boomers, Gen X and Millenials are simply older and most are married. Your smash frequency goes down. If you and your wife smashed 5x/day every day, it's eventually going to drop to 2x/day. Life gets in the way and there's only so many ways to smash the same person.
Gen Z - they fukk less for many reasons, mainly because they socialize less in person. Gen Z broads can pick and choose the top shelf dudes when they need to be piped plus they have access to the best sex toys. Regular/normal Gen Z guys aren't interested in chasing women they feel they have zero chance of pulling. More scared but strangely they have more pride.
Porn - instead of bugging your GF for some booty, dudes just put on some porn, rub it out and then go back to playing Madden. This applies to every demographic.
If you gave the average man a harem of 100 women...whatever races, body types he wants...he'd be smashing ALL THE TIME. I don't think desire went away. Just opportunities.
