This takes a bit of working out (at least for me) but I am guessing that building these dwellings on a rise provided the opportunity to integrate a garage at the front with the lounge being above it, and accessed by stairs. It's a bit unusual and it wouldn't appeal to everyone, least of all people who find stairs challenging. I've had a couple of houses with adjoining garages and a whiff of petrol indoors was not unknown either.

Yes, a split-level Bungalow - ours only had five steps.
No, I don't remember smelling fuel or other fumes in the house.
.
After I was married, our second house we lived in had an integral garage and I could just about hear the car engine, but again, no smells in the rest of the house.
Maybe because we always left the door open for a while for ventilation ?