I've seen other issues with Avis corporate and non-corporate locations not working together, including regarding switching cars if your rental car has a problem. I was once told by a non-corporate location that I would have to drive 200 miles to the nearest corporate location if I wanted to switch my airport-rented car.

So this is probably due to the airport locations being corporate and the non-airport locations being non-corporate.

Avis is annoying in that they seem to treat non-corporate locations as if they were another brand, but they still use the same Avis name.