Well, for starters, think of this:
Where do the eggs, the meats, and the poultry from your supermarket come from?
There were roughly 5000 slaughterhouses in America in the 70's, take a guess as to how many there are today.
Guess how many meat packing companies there are that are competitors in the market.
How much sway does McDonald's really have over the meat, poultry, and potato markets?