What's so hard to understand. (Oops, I forgot that there still are some Reganomics supply-siders out there.)
When the turkey demand is high, suppliers bust their asses over producing to meet the demand. The price drops because of that overproduction and because the suppliers won't know what to do with the birds after eat-turkey season, so everybody eats cheap turkeys during eat-turkey season.
When the turkey demand is low, supplies have no incentive to produce turkeys, so they don't. (You don't really believe that turkey farms have the same number of turkeys growing in them year round, do you? Seriously?) So the low supply means higher prices during non-turkey season.
The bottom line is that our economy is DEMAND DRIVEN. Always has been. That's why supply-side, Reaganomics economists suck green eggs. You come up with a newer and better way for what people demand (e.g., more information, faster), and the demand will THEN be supplied (computers). Try supplying something that nobody wants, and see how that does it for ya.