As a pedestrian tourist with a frequent need to pee, in general there are very few public toilets in Western European cities. Bus stations and shopping malls are amongst the few reliable refuges.

Cost appears to be the reason. Plus presumably pursue from local businesses which feel they 'lose' custom if people can pee for free instead of having to pay for a coffee they don't want just to use the loo..

Where you can eat or drink, there are going to be toilets, you won't get a concession without them, besides for small snack bars. The issue is probably mostly caused by the way home, because outside of restaurants, bars and larger shops and malls there are indeed very few public toilets.