It is very much a generational thing, as others have said. I'm 64. Group showers and being naked in the locker room were normalized from the time I would go swimming at the Y in grade school.
At the college where I teach, when I arrived in the late 1980s students shared a locker room with staff and faculty, including a sauna in which we'd all sit naked, and open showers with posts with several shower heads on each. Students often showered and changed after P.E. classes or working out in the evening. It was normal to see students from a class I was teaching in the showers, sauna and locker room--something that would be almost unthinkable now, except for guys from the swim team walking from their locker room through the main locker room to the pool.
By the time of the covid shutdown, the sauna had died of old age and was not replaced. Someone donated a lot of money to create a new showplace of a fitness center. New student locker rooms were built with individual curtained showers, and my sense is few students change or shower unless they are using the pool. Faculty and staff use the old locker room as there is no private-shower option, everyone uses the open showers. There us much less use than before covid.
It seems to me that the it's a combination of increased awareness that being forced to be naked in front of others is traumatizing for some kids, an awareness that there are indeed gay or lesbian people in the locker room, some of us being inappropriate with staring, the ubiquity of cell phone cameras and spy cams and photos that have been leaked/spread (imagine being in middle or high school and someone shares a photo of you naked in the locker room or shower), and the highly publicized cases of sexually predatory coaches (like Jerry Sandusky) that has led to the demise of mandatory group showers in middle and high school. And then people never get comfortable with being naked around others in a locker room the way most of us did.