History books say that after the fall of Rome, 'we' lost our understanding of their technology. But aqueducts, lots of Rome's buildings etc were still standing, monasteries had washing and toilet facilities, castles and palaces were built. Why were even the rich apparently content to live in stink, sit in windy garderobes etc? - you don't need more to see what I'm getting at. In fact was this the state of 'Europe' or were there wide differences?
Part of the answer may rely in the fact that post-Western Roman Empire European nobles/royals were not descendants of older established noble families, but were often warlords from what Romans would have considered "barbarian" tribes. They grew up in tribal, sometimes semi-nomadic, environments where sewerage and running water were not known or considered "must-haves".
They didn't have it and didn't know they wanted it.
What I say would apply mostly to the beginning of the Middle Ages and they gradually adopted higher standards.