That still doesn’t explain why for example, the romans gave us a start regarding roads, sewers, bathe etc. but then we just turned our backs on it?
Simple.
Mistrust, war, stealing the dressed stone for their own building ideas, religion, myths (Roman London was virtually left to rot when the legions pulled out) but the main thing was the Saxons and Vikings. They had their ideas of housing, wooden mainly, and hardly used the Roman buildings. They had their own ideals, Gods and way of doing things. A society of hot baths, sewage systems and heated rooms wasn't in their plans.
Plus the knowledge that the Romans possessed just melted away. Legions go, many craftsmen leave as well due to the incoming Saxons. It was only the rich who really lived with hot water etc etc anyway so the great unwashed remained just that.
Take Fishbourne Roman Palace.
The largest know Roman palace north of the Alps. Very close to Chichester, itself a Roman walled town. Fishbourne had bath houses, heated rooms, mosaics etc etc on a very grand scale. Then it had a fire, probably got caught up in the Caraucius revolt, more fire and then left abandoned with it's stone being robbed by the good citizens of Chichester. Legions go, Chichester, inside the walls, remains mostly unoccupied until the 9th century when Alfred the Great gets threatened by the Vikings and orders the rebuilding of old Roman walled towns. Normans come some time later and the City rebuilds again, Castle etc etc. Except they don't rebuild the fancy stuff like bath houses. The technology is lost to them.
Rinse and repeat countrywide.