Ask any guy who grew up in the 1950's and belonged to his local YMCA and he'll let you in on a well-known "secret." Guys used to swim naked there! Moreover, there were often "solariums" or outdoor sunning porches where nude sunbathing was common. Old and young, grandpas, dads and their sons, those in shape or who needed to get in shape, had one great equalizer: you swam and sunned in what God gave ya.
Sometime, perhaps during the 1960's or so, things began to change. No doubt it had some to do with going co-ed. Then it became more difficult to avoid an awkward, unplanned, "meeting of the genders" if a female opened the wrong door or showed up during the men's swim hour.
But the change also probably had much to do with the ways society was morphing too. The sexual revolution made some circumstances take on a sexual dimension where there hadn't been one before. Decades later, many adults had come to be very uneasy about being nude in the presence of minors, even in the locker room and showers, due to growing awareness of the problems of abuse.
Consequently, nudity is disappearing in many changing areas and the group shower room has been replaced with individual cubicles. It's a bit sad, actually. The same camaraderie created by the "corporate nudity" characteristic of a Finnish sauna is unknown to many Y patrons today.
There will no doubt come a time when someone will write a blog entry that starts "Ask any guy who grew up in the 1970's and they'll tell you a well-known 'secret.' Guys used to take group showers naked and change in open rooms there..."