Taking a plastic bag with you to lug around garbage is obviously inconvenient. They could just put up public garbage cans like most of the civilized world.

The hotels and public venues also had the cheap single-ply stuff.

I was not able to find any decent tissues in stores, so I doubt that people all buy the good stuff for their homes.

In cities, I agree that if you aren't used to it, it might be inconvenient.

However, 99% of hikers in Europe carry their own trash bags. It took off in the early 2000 and now it's almost a culture thing, especially amongst young hikers, and not having one is basically a social error (well, littering is, you can always ask people for an empty trash bag if you forgot yours). Honestly I can see why they choose that solution.