As someone who has needed a scooter at WDW:
I see this comment all the time. It used to be me saying this, until I was this situation. I tore my MCL 4 weeks before a trip to Disney. It a severe tear, but not something they could go in and fix, so it had to scar down on its own. I had complications ,and it was nearly a year before I could walk long distances. I needed a scooter for 2 trips.
It was painful, and I was very limited mobility wise. I sometimes needed my Husband or daughter's help to dock the scooter or to get on and off to get seated on the bus ( scooters can and do tip on buses, so if you can transfer to a seat they ask that you do so). Also, It would have likely been a disaster if they had needed to go to the back of the line and had gotten separated from me by not being able to get on the bus. Yes, loading 12 people with a scooter is excessive, but please consider that the handicapped person might need assistance from family, and that families want to stay together. Also, we load first, but get off last. Well after you are gone. It takes as much time to get the scooter off as it did on, and my family had to wait for that.
Until you have been in their shoes, you don't get it. I certifiably didn't. Most people think a scooter is a free pass to the front of the line, preferred viewing, ect. It's anything but. It often means more waiting at rides. I couldn't load a lot of things unless they were slowed or stopped so my family was constantly waiting longer for that to happen. There were a lot of rides I simply could not do because I couldn't load. It makes pretty much everything at Disney exponentially harder. I HATED using it. I hated the glares I got when people had to wait to get on the bus so I could load. I hated being looked at like I was just lazy. I hated having to use HC viewing locations to be able to see anything except the seat of someone's pants. I hated the looks I got when rides had to be slowed or stopped for me. Navigating crowds without hitting someone was nerve wracking. It's not a fun experience.