I don't understand the need to tip to use german bathrooms

I don't understand the bathroom situation in stores, some restaurants, some museums and other places in Germany. I may have written about this earlier but felt that I had to express my indignation. The whole situation is quite strange. You are in a store or a restaurant and need to use the bathroom and what you always see before entering is an anteroom in which stands an attendant by a table with a plate where you are supposed to deposit a tip for being able to use the facility. The attendants are paid by the establishment; they all receive a salary for doing janitorial work. And they want a tip for having to pee? Very bizarre. Some even get angry at you if you leave without giving a tip.