That initially sounds like it makes sense, but in reality it doesn't. For any bathroom facility there is already a relatively fixed regular cost being applied

That initially sounds like it makes sense, but in reality it doesn't. For any bathroom facility there is already a relatively fixed regular cost being applied to maintain them. As free bathrooms are nearly always funded by community purses their existence is justified by usage, whereas paid bathrooms are nearly always funded by commercial entities which justify their existence with profit.