I stayed with a german family who wore socks and sandals in their house- like they would see me in my socks and ask me if I couldn't find my hausschuhe. It was mortifying.
I grew up in a household where we were expected to take off our shoes upon entering the house because our shoes were usually dirty.
If I ask someone to take off their shoes at my apartment and they refuse, they are leaving.
My theory is Americans used to be normal, but sitcoms had people keep their shoes on because it would be boring and disrupt the flow of a scene if every time someone came in they had to take their shoes off, and that's why Americans think it's ok to keep your shoes on indoors now.
Many Americans do, but it's the reverse effect: Sitcoms started showing people wearing shoes in bed, so Americans followed suit. It's the same thing that happened with Americans facing their books the wrong way on the shelf