Had an interesting discussion with a younger adult the other day. He sees any display of masculinity as "gay". Straight men don't wear fancy underwear, that is for gays. Straight men don't shower naked, that is for gays, straight men don't walk naked in locker room that is "so gay".
So in essence, it appears that it is really a fear to be seen as gay that pushes the younger generation to avoid showing their genitals or sexy underwear in locker rooms and showers.
It would be interesting to make a corrolation to see if towel dancers tend to wear boring underwear (loose boxers, white tighty whities, loose boxer briefs) while those who are not affraid to shower naked wear sexier underwear.