I bet they freeze frozen chicken breasts before throwing them all in a bag together. Or maybe it's the fact that chicken is poultry, and the pieces can freeze together in a bag without sticking to one another. Red meat is apparently different.
I purchased a package of pork chops because they were cheap and I wanted an excuse to buy sage. I cooked up a couple of pork chops (they turned out well), and went to freeze the rest. As I commonly do with leftovers, I put them in a gallon-sized Zip-Lock bag and threw them in the freezer.
The next time we had pork chops, they were prepared in the oven, as one big multi-pork-chop mass. I'd worked for about fifteen minutes to get even one chop loose from the pack, but the chops wouldn't budge from each other. After a lot of swearing and sweating, I slammed them down in a pan, put some spices on them, and threw them in the oven for an hour. They weren't bad.