I mostly see the pay showers at campgrounds where there are a lot of tenters or backpackers.
X2, as well as beach front campgrounds where you are apt to take more than one shower in a day, or shower kids due to the salt water. Until we had an RV we were more than willing to pay for a hot shower-wasn't that expensive back then but energy costs weren't out of sight, either. Higher costs also discourage wasting water. Even when I had elbow length, thick hair I never took more than 10 minutes for a shower.
One of the reasons we started RVing was to avoid having to use a communal shower. But if the situation warranted it we'd use them, gladly pay, and understand the campground is a business not a charity.