Nothing is more illustrative of the change in adolescent attitudes than UW. For generations of kids wore white jockey briefs. It was the de facto standard underwear for anyone under 20. In all the years I was in school I never saw anything else. Boxers were considered only for adults- and rather old-fashion at that. Boxer-briefs hadn't been invented.
Then when I was in college circa 1970, colorful 'bikini' style UW from Europe became popular. The idea seem to be as little as possible. In fact, some guys started wearing none at all.
How different it is now. Add to this, the long baggy swimsuits, floppy pants, and "shorts' that hang down below the knee- so many examples of how bashful young males are about showing their bodies these days.
I have even seen boys wearing shirts in the swimming pool these days.