One thing that never ceases to amaze me is the busses where I live here in Chicago. They pick up citizens with wheelchairs and ECVs usually within about 1 minute or less. The bus bends down, a flap flips up and out the front door creating a ramp, they roll on in. The bus driver then asks two people to vacate the third second and third seat right behind the driver. That's because the thing lifts up and folds, and hooks are exposed on the back of the folded up chair bottoms and the metal floor planks underneath them. They hook the hooks around sturdy parts of the chair or ECV, ask the person using it to put it in a locked state with brakes applied, and that's it. This all happens in under a minute. I see it happen at least twice a week on my part time commute through the city for a job not near my home location. If there are multiple people waiting for a bus, they've got another one of these setups right across the isle. If more than two are waiting, oh well, you get to wait for the next bus. The hooks are simple, very tough, and crank lock in place so the cables they are attached to don't unravel. This all happens on a crowded city bus. Two people are asked to move, that's it. Since we're all so used to crowded busses here in the city, we just get up, no big deal. Little to no irritation caused.
Disney's system is a bit different, and is designed to offer the safest journey to everyone. However, sometimes it takes quite a while to load up passengers because people are asked to transfer out of vehicles sometimes. That's potentially more difficult than the physical loading of the vehicle itself.
One other thing, nobody mentions that the "last" people to get off the bus are the people who needed to be loaded first. They also may be stuck for an additional 5 minutes to transfer back into their vehicle if that's what happened. Sometimes this even requires a two man lift if the person is incapable of assisting in the process. Though I must admit, anyone that needs a two man lift is likely in a wheelchair, electric wheelchair, and not an ECV.
Disney does play it safe to be sure, but remember, not every bus driver comes from the same mold either. I saw a driver load two ECVs with transfers in seriously two minutes one morning at Pop. I had boarded the bus already, as the bus driver had been at the bus holding point when I asked him which bus he was, and he was waiting to be a Magic Kingdom bus. He asked me if that's where I was going, and it was. So, I was asked to board, why not? I'd have to find the stop otherwise, and I'd run into him a few minutes later asking the same question again. When he pulled up and started loading those ECVs, I was amazed at the speed and efficiency. He just had it down perfect. But, the people using the ECVs were also very with it, and added to the efficiency. This guy was also not taking his time, I could hear hurried steps as he entered the bus, loaded, went out, loaded again, and finally closed up the ramp and let everyone else in. Some people who drive also may be in a position where performing the loads may be physically challenging. If you're a retired Florida resident driving a bus, you're probably not going to be super fast at this sort of thing, but with good reason.
Does Disney ever operate double length busses with the accordian partitions? In Chicago, we've got busses that are double length and can bend in the middle. This is great for busses headed down to Wrigley Field or the museum campus. If they don't have them, DIsney needs to get a few to use for end of day crowds.