Most of the time, and this isn't always true, but most of the time when you get in an elevator with a family using a stroller there are multiple adults together. Before they get on they fold it in half (as many do easily these days) and one adult holds the kid. Many do it it this way and are obviously taking the small elevator spaces into account. Being considerate of others.
In my ten cruises I have seen very few people hauling a baby bag, a sippy cup, a stroller and a child around the ship. There is little need as the room is always a few steps away. Not many people use strollers on the ship and that's just a fact. You see them hauled on and you see them hauled off. You see them used for excursions. For all the children on a
Disney cruise there could be a zoo of strollers but there isn't. They are simply not required all of the time.
As to your wheelchair statement they aren't even CLOSE to the same thing. I'm disabled. I know the difference.