Hell if I know.
The delta between kosher and non- seems to increase the further you get from further processing.
It could be classic "over a barrel" behavior. Despite the "no big deal/thanksgiving is wrong" contingent among orthodox Jews, there's got to be a decent market for "must have whole kosher turkey" at thanksgiving. That market is over a barrel.
Another mechanic at work (possibly) is that as other steps of processing are added, the total premium you pay dilutes the impact of the kosher premium.
So if you're already doubling the cost per pound, (just hypothetically to display the math,) and you start at $1.50 vs. $3 per pound...
Then you charge $1 per pound to cut up turkey...
you get $2.50 per pound vs. $4 per pound. The kosher premium appears to begin to go away.
However, the .50 difference you're talking about < the original kosher premium, leading me to believe that the kosher premium at the outset has a lot of give in it.
But then again you're comparing before TG vs. after TG. Demand for turkey of all kinds falls through the floor... and you pretty much have to get rid of this perishable STUFF any way you can, no matter how you slice it, drain its blood, etc. That could explain taking a comparative loss on it after Turkey day... especially given that nobody has a "Hannukah goose" tradition to substitute turkey for.
PFnV