this seems really dangerous for anyone who might get stranded.
I'd take a step back and say no, this isn't actually as bad as some of the comments seem to suggest.
The vast, vast majority of building emergencies are safe to shelter in place. Modern building codes generally prevent fires from spreading too far, and isolate smoke to a specific place in the building.
Then, for certain types of catastrophic disasters, being able bodied doesn't actually help, as people can still get stuck and need rescue from firefighters anyway.
You need some kind of disaster Goldilocks zone where things are bad enough to where quick evacuation is helpful and things aren't so bad that evacuation isn't feasible, before it starts making a difference.
And in those situations, many buildings do have evacuation chairs in the stairwells. And stronger people can assist carrying down the stairs, too. There are a lot of variations on two-person or single person carries that depend on exactly what mobility limitation there is. If you live or work with or around people with mobility issues, it's worth looking them up, maybe taking a first aid/survival class or something.