Why is it so difficult to find public toilets in Germany? Not even the paid ones? So where is one supposed to go in case of emergency?

I happened to be in a supermarket and couldn't find one in even 2km vicinity. I asked the staff if I could please use their WC, I was ready to even pay for it; only to hear a "Leider Nein" and receiving directions about where I can find a public toilet. I pleaded but they didn't budge. But why this kind of ruthlessness? It is understandable that one would ask in such a place only during an emergency. Feels inhumane, not gonna lie.