This study does not address hormonal changes, but I'd like to see the secular testosterone decline studied. Testosterone directly mediates sexual desire, so that should play a role.
I think this is the reason too. There could be many possible reasons why young men have less testosterone than their ancenstors. Maybe the high child obesity rates? Chemicals in foods?
The high obesity rate is both caused and causing the lower testosterone. Endocrine disruptors (estrogen-like chemicals everywhere, not just in foods, originating from plastic manufacture, among others) are the biggest suspect IMO. They're probably causing both obesity and testosterone decline. It's an emerging topic of research with growing evidence.
I think in a century we're going to be looked upon as barbarians by our ancestors for some of the things we did to our bodies, just as we look upon the earlier generations who leaded gasoline, or smoked pervasively.