You know I think this has to do with liability and insurances.

Cars can drive up and hit a pedestrian or someone in a wheelchair ...so
those rules exist.

Seems with this situation some compromise could be made?

He could wave to them, and they could come outside for him at the front door or something like that?

I have worked in pharmacies with drive thrus. We will not attend or allow
pedestrians who walk up to the window. We were told not to under any
circumstances. But no one in a wheelchair ever attempted it.

I would write the corporate offices...and if that were negative, then I would continue thru the newspapers. But the bottom line is probably a clause in the liability contract of the insurance carrier they use. If that clause is violated, then liability is forfeit if an accident occurs (a car strikes the wheelchair).
Design of the approach to the window may obscure the wheelchair and person in it, so a car could accidently not see them.