It's a matter of scale. Tyson and Cargil don't spend several billions of dollars to develop a new cut of bacon, essentially one SKU at the supermarket. However, Pfizer and Sanofi will spend billions to create one new drug.

Also, drugs do get super cheap once the patents expire. In fact, there are massive companies that do nothing but wait for patents to expire so they can make generics—take a look at Teva and Perrigo if you're curious about the model.