You can't look at tolerance for open drug use in isolation. It's part of a complete system that includes a social safety net, access to medical care, treatment for mental health issues and the initial conditions that cause people to become drug dependent in the first place.

Europe understands that people are entitled to and deserve a basic standard of living. It largely explains why the EU has expanded eastwards into former Soviet bloc countries where people are much poorer. The EU as a whole takes an economic hit for that but it's an undeniable good for those poorer members.

Whereas in the US, people seem to be stuck in a 19th century "every man for himself" frontier cosplay.