You mean pork bellies as in a bacon, lettuce and tomato sandwich?
I think it has to do with the evolution of the livestock industy, larger producers, factory farms and integration with packers and producers. Risk management is shited to input costs, grains, efficiency of operations and the widespead use of illegal labor in packing plants. Not a lot of huge end users of pork compared to beef, McDonalds, etc....
That was the first pit I ever saw in person, 5 years old when my dad worked for jon morrell.