My parents too moved to a house when they retired that had the entire living space on the ground floor and a loft that my mother turned into a sewing-room, so she could get away from television! It was too cold to use in the winter, as she was too mean to heat it, so come the first spring, she no longer could readily go up and down stairs.
We in our turn moved to a house with stairs, so we both still manage them, but DH due to poor health spent far too much time during the day sitting on his sofa, and is now working hard to regain, not his ability to manage stairs but to walk 500 yards on the flat.
So yes, bungalow legs is a thing, but having a house with stairs is no guarantee that other forms of motion will remain possible. Even if you have no health problems, it seems to be a case of "use it, or loose it" as we age.
Kircubbin, I hope you can get help with your hip, and please do check with your doctor or a physiotherapist which excercises you can do, and which you should not do.