It's a question of property right. In particular, the shared property of the common parts of a city. For the private parts of a city (eg. apartments), they us

It's a question of property right. In particular, the shared property of the common parts of a city. For the private parts of a city (eg. apartments), they usually include toilets, and you expect your guest to use them instead of shitting in your kitchen or living room. Similarly, as _owner_ of a share of the common parts of your city, you have the choice of providing public toilets, so that guests, visitors, or just citizen far from their home can be expected to use them, instead of shitting in the public space, thus degrading the bacteriological common space (feces can transmit some bad illnesses https://en.wikipedia.org/wiki/Fecal–oral_route https://en.wikipedia.org/wiki/Fecal–oral_route ).