Hmm... Seems I might be the odd one, as we've been to a LOT of private campgrounds in New England with pay showers. I would estimate it tends towards more than half the campgrounds we've been to around here. The Connecticut state parks we've been to don't have pay showers, but do have a simple and effective "push button" water timer to help prevent wasting water.
When I've asked campground managers about pay showers, they always say "to conserve water"... but I think that is mostly baloney, as I said previously it is perfectly easy to install simple push button showers.
I do consider pay showers a negative when staying at an expensive private campground/resort.