Interesting comments you mentioned, and thank you for sharing your experiences with this topic. All I can guess is that the rules must differ from state to state. I looked up our transit system's rules for wheeled mobility devices on the buses, and the bus driver is required to attach 4 securement straps (for wheelchairs), and 3 securement straps for scooters (ECVs), to the frame of the wheeled mobility device. The passenger remains seated in either the wheelchair or ECV for the duration of the ride.
(I put a picture below of one of our city buses, showing the folded up seat for the wheeled mobility devices, and the red, securement straps. (In front, to the right, you'll see a black shaded area--that is a 2-3 foot square, black block, about 3 1/2 feet high, and it is directly behind the bus driver's partition. Not sure if that is some sort of safety barricade for the driver, in case one of those scooters, for example, got loose--which I highly doubt would ever happen.) By the way, I've never seen anyone not give up their seat for a handicapped person; most people I've seen on public transit have compassion, and I've been riding the system for many, many years.