No one has answered the question of whether or not this is a gender thing so I'll try. Before WW2 no one took showers because no one had then, mostly. For reasons of time, space, and cost, the military offered nothing else. When the war was over and the troops came home, young boys looked at the 'real men' who had won the war and saw that they preferred showers, now. (WW2 also destroyed the men's pajama's business). This kind of thing is more important than most of us think. The trend started then is still going strong.