This is what one major cat food manufacturer has to say on the subject :-
While we do incorporate pork as an ingredient in some of our pet food products, we do not manufacture any dog or cat food products with pork as one of the primary ingredients. There is no reason from a nutrition standpoint not to use pork for pet foods. However, market research studies indicate that there isn't a lot of consumer demand for dog or cat food products which contain pork as a primary ingredient. Should that perception change, we would re-evaluate the use of pork as a primary ingredient in pet food products.