Back in "The Day", the whole group shower thing was considered a "right of passage". It was not only Expected, but Promoted, even Enforced.
I believe the prevailing theory was it would "desensitize" you to being naked around other guys. Force you to confront, and overcome, your insecurities. "Toughen" you up. Wipe out any curiosities, or sensationalism, about other guys.
They were likely getting us ready for the military.
Of course, that didn't always work out that way. A few guys ended up being traumatized. In general, though, it accomplished the desired effects.
My first school "let's all get naked" experience was
Freshmen PE class. Before that, it was the public pool changing rooms, camp ground showers, sponging down while camping with the Cub/Boy Scouts (strictly outdoors, no formal accommodations), and skinny dipping with my buddies after damming up the creek.