The Awl has a fascinating analysis of the McRib that includes some speculation on why McDonald’s introduces it when it does. The above graph, from the article, plots two lines,
The blue line is the price of hogs in America over the last decade, and the black lines represent approximate times when McDonald’s has reintroduced the McRib
It goes into details on why McDonald’s might introduce the McRib when it does and why. It has other things to say about the sandwich, not all that I agree with, but overall the article is thought provoking and well worth a read.
I would also add that besides price, Marketing cycles have something to do with it. McDonald’s is constantly turning over promotions, and the McRib would likely have to be tied into that campaign cycle as well.