I know I had to submit a letter from my doctor, detailing why I needed the handicapped room. That was the only way I could secure one of these rooms. How are others getting the rooms unless there has been no one in need requesting these rooms?
The other thing you need to remember is this: You may see someone walking around the ship and then see them go into a handicapped room. What you might not be seeing is that there is a wheel chair in that room and is only used to go longer distances. Maybe they can walk from the room to the pool but not all the way to the dining room. And maybe they can't stand for long periods of time and use the roll in showers. People don't always think there is a need for these rooms but they don't know the full story.