The Way Homes are Built
Europe is old. Yeah, we said it. Like, really old. Most of the structures there go back hundreds of years, and back then, well, builders just did things differently. The materials were heavier and stronger. This has made it difficult for some upgrades like proper plumbing to be implemented in many places.
In the U.S., the homes tend to be significantly newer than those in Europe. As such, new, cheaper materials are used to build them. This European claims the walls felt like they were made from paper which is a bit of a stretch- unless your upstairs neighbor has a drum set or a two year old.