Where did you see this as I have never seen it anywhere that they are supposed to be the first unloaded.
The
Air Carrier Access Act regulates disability assistance/policies for people with disabilities traveling by air
This is the text about timely return of wheelchairs (my bold)
(d) In order to achieve the timely return of wheelchairs, you must ensure that passengers' wheelchairs, other mobility aids, and other assistive devices are among the first items retrieved from the baggage compartment.
In our experience with gate checking a wheelchair, the gate checked items usually come kind of all at once and usually take a few minutes after passengers start getting off the plane. Whether all the wheelchairs come up before every stroller is deplaned seems to depend on how things were packed in the baggage compartment.
We always receive our daughter's wheelchair at the gate, but when we go to pick up our bags, we see wheelchairs that were not delivered to the gate come out on the carousel before bags (passengers can choose to have their wheelchair delivered at the gate or sent to baggage claim)