If you have mobility issues that prevent you from exiting your building easily then you can move somewhere else. We don’t need to make every apartment building in the country more expensive for this extremely specific scenario.
I can go up and down unobstructed stairs without any issues, but I have back problems which keep me from doing heavy lifting and I'm in no condition to jump or climb over a sofa in the middle of a flight of stairs.
The real problem here is expecting people to be able bodied enough to deal with a lack of alternative exits when someone in the same building inevitably is careless enough to start a fire.