From personal experience (my disabled son Kevin) the bathrooms are bigger to allow for wheelchair manuverability. To enable tranfer from the chair to the pot and back safely. And to allow the privacy anyone else is entitled to by having enough space to close the door completely behind you. Consider also that the disabled person may require some help in transfering and cleaning up afterwards, requiring room for another person in the stall.
There are a lot of factors to consider with the differing degrees of dis/ability.
Until you are in a chair or accompany someone who uses one daily it's kinda hard to relate.
We've had some very ---smurfy--- experiences dealing with different arena and public entertainment venues, never mind the normal daily obstacles.
The horror stories, OY!
The ADA is very much worth reading if only to educate yourself.
Depending upon where you live we still have a long way to go!
And with the general population living to be much older it's very likely to become an issue in YOUR life somewhere down the path.
Don't get me started!

FYI, Kevin pulls his chair up to the arcade machine as close as he can get, leans forward and makes it his ---smurfette---!

ARCADIAC!