IMO sex is simply overrated. A guy can go online anytime he wants to and jerk off to porn, he can see hundreds of pussies every single day. If he goes out and tries to chat with new girls, he usually gets shot down, rejected, and if not he is having hard time. He's got to learn game, which takes long time, and the progress is usually not that easy. Porn is simply very easy escape from harsh reality of dating and rejections.
Technology doesn't help at all, people can "connect" to each other in seconds via internet and phones, yet the reality is that most became more distant. People spent hours and hours online instead of communicating directly to each other.
People are more selfish, more egoistic, more attention seeking (see above, e.g. selfies, instagram...). Many times it is difficult to truly connect on emotional level with somebody who is only concern about himself or herself...
People got more fat. Guys got fat and lazy. They don't want to move, they don't want to play sports, run around, lift weights... They rather sit home, eat pizza, drink sodas and play games. A guy who play games for couple years has multiple-fold less social skills than guy who interacts with people... The thing is, this overall behavior decreases levels of testosterone, guys are simply less horny and less skilled in communication. Also, because of the accumulated fat they also have too much of hormonal imbalance, too much of estrogen metabolites in blood. Estrogen is female hormone circulating in male's body... In other words, guys became more girly, weaker, softer, fatter... Which in simple words translates to less attractive to females...
Girls got fat and lazy as well. Fat(er) girl is not as attractive as skinny girl. There is a difference if you see a girl that is 5'5" and has 170 pounds vs girl tat is 5'5" and has 115 pounds. Not mentioning girls with 200+ pounds... Girls did, however, gain lots of feminism, more independence, more self-sufficiency. They are allowed to be more dominant, to make more and more choices for themselves... They gain lots of classical male power, thus they don't really 'need' males, especially not weak males...
So sex itself is no longer as attractive as it used to be. It involves hard work of approaching and contacting strangers (women) while facing easy rejections, emotional suffering through flakes and rejections, overall lesser desire for females, and lesser attraction of both males and females...