Tiran saidI realize I am asking a generality, and this thread will likely either be ignored or degenerate into the usually trolling, but I am hoping to get at least a few actual responses.
This question gets asked periodically here, in various forms. The athletic supporter was invented in the late 1800s as an answer to male discomfort when riding the newly-invented bicycle. In fact, the oldest jock manufacturer still in existence from that time, Bike, was named for that reason.
Until then men's underwear in the West was loose and unsupportive, consisting of either full coverage knit Union suits, or baggy "drawers" that were the prototype of modern boxers, often attached at the waist to a short-sleeve undershirt that held them up. Because what they all lacked was elastic waistbands and form fit.
The jock provided the support men wanted on a bicycle saddle, and soon realized it had other applications as well, to include horseback riding and general sports. Modern elasticized underwear does much of what a jock does, reducing the need for a special athletic garment, although I still find a formed, ventilated pouch better than briefs that jam your sweaty stuff flat against your body.
The other reason for the jock's decline appears related to the new modesty that has become common in men's locker rooms. Lots of speculation why that is, but the end result is that briefs show less skin than a jock.
The ironic thing to me is that in my own youth it was "real men" who got naked together at gyms & swimming pools without giving it a thought, and only "sissies" who were shy, accused of acting "like girls" (euphemisms for queers). Today it's totally reversed, and if you don't do a towel dance and you use the gym gang shower without hesitation then you're gay. And I really don't know how this change came about.