I think that was true during the preview.
Cheshire Figment had spoken with a supevisor there and it sounded like it was a situation of the CMs needing to get familiar with the attraction and with loading the wheelchair car.
If they use just one wheelchair car, they have one whole ride cycle to load before that ride car comes around again for unloading. If the use 2 wheelchair cars, spaced half the ride apart, they have half the ride cycle to load. From what I understand, it sounds like if they add 'regular' cars, it shortens the time they have to load.
I know, for example, the first few times we rode in the Imagination wheelchair car or in the Buzz Lightyear car, it took a long time for the CMs to load DD's wheelchair. The last few times we rode Buzz, the CM didn't even slow the moving walkway - she was that fast.
It's really discouraging when they make people board at the handicapped boarding area that would not have to board there if they hadn't put steps into the 'regular' line. We have no choice but to wait for the accessible car, but I know how frustrating it is to see the 'regular' line boarding people who were behind you. It must be even more frustrating to see that and know you would be able to board that car, if you could get there.