It's likely a correlation between:
Amount of processed foods eaten
Amount of pesticides on and in foods
Amount of environmental synthetic birth control hormones
Emphasis on high carb, low protein, low healthy fats consumed
Amount of seed oils consumed
Lack of running around outside growing up
Houses being too well sealed/never experiencing hot and cold extremes
Poor sleeping habits
Being fat (effects aside from poor eating habits and bad foods, it's really bad for people) 
Lack of fitness
Too much medication
Lack of healthy gut biome
Not eating traditional fermented foods
Too much alcohol
Too much cannabis
Too little motivation toward actual physical sexual relationships (probably from much too young exposure to porn and all the beauty influencers) 
Too much social media leading to dopamine addiction
Et cetera.