First, it was the A300 line they restarted for FedEx and then continued for UPS, not the A310.
Second, as I said, had UPS and FedEx not bought the Airbus products, France wasn't going to give them the landing slots they needed and allow access to certain markets they wanted to expand into. Thing that the guys at UPS didn't understand is why the company not only bought the A300's, but bought 94 of them when they only needed 24 to fill the planned European routes and then put all 94 aircraft in the US domestic schedule instead of bringing home the 767's that were being used in Europe. At least FedEx didn't have anything of that size (techincally since the DC-10's can carry a bit more) and they spread their A300's across the system. No one I ever talked to was quite sure why the A310's were purchased by FedEx except that their original plan for buying some 757's fell through and the A310 was about the only other option and at least had some commonality with the A300-600RF's they bought and pilots get a common type rating.