Who really does fast food pork other than bacon? I'm looking at what Panda Express has on its current national menu, and there isn't a single pork item. They might have had some in the past, but I'm guessing it doesn't sell well.
I know people from China. And I agree that it's hard to call Panda express "Chinese". I remember a friend originally from China telling me about going to a Panda Express with her parents because they were in a hurry on vacation. They weren't quite sure what it was, and her dad asked if it was Japanese. And sweet and sour pork in that style with the bright red sauce is definitely meant to appeal to American tastes.
But yeah - pork is the most common meat in Chinese cuisine. It's well suited for growing conditions in China. It doesn't take a whole lot of room and they grow quickly to market size. Beef cattle need room to graze.