Late fall was traditionally when the pigs were slaughtered because they had grown all that they were going to that year on easy local grown feed (you really weren't gonna pay to buy feed to keep anything but one boar and the best young sows over the unproductive winter months).
The weather was cold enough now to preserve the meat during processing until it could get salted down for long term storage and the summer harvest was over now and the all the farm people were available for slaughter duty.
Pork prices still follow the seasonal dip as relatively more mature pigs hit the marketplace and when pork hits "dead bottom cheap" (beats the price of beef) the McRib comes back.
(yup, it's made up of all them little bitty pig noses and wee little pig toeses and them plucky little bitty pig peckers that the slaughter houses have to figure out how to do something with -- can't make but so much Neese's "sausage" bricks outta all them little bits and modern hot dogs are mostly beef now days so the McRib has jest gotta come back fer a little while to use up all them little pieces)
If you are the courageous type, pluck apart a chicken McNugget or a McRib to see what it is really made of ....