It's worth noting you do have to pay for virtually all public toilets in Turkey.
Charging paying customers at your bar and restaurant is very different.
Buzz Bar in Oludeniz charges non customers 1TL to use their toilets and has done for years - but customers do not have to pay anything.
I think this is just to discourage every tom dick and harry coming in off the beach and using their loos to wash themselves off, sand and all which is understandable and I don't think it is particularly enforced.