I don't know where they did this study I see lots of women at the gym.I would say that women out number men at most gyms as well.
Also a lot of people will simply wear their gym clothes to the gym work out and then go home to change and shower so if you have an issue about being around other people it is easily curable.
The 20 man showers in basic training and tech school never bothered me really of course I would prefer privacy given the choice I never saw the big deal you have what everyone else has
so scrub your ass with some soap and be done with it or change your clothes and get going no big deal really.This kind of thing seems to be an issue for some in the US for some reason I think it is a combination of people lacking self confidence and homophobia.
The people they talked to seriously lack self confidence I mean who the hell cares if your co-workers has a tattoo on their butt? "Oh my god another human body before my eyes must feel awkward because of ...something." Really people need to grow up and stop making a big deal out things that are not that important.
This really is a an American thing to by and large.