Turkey?
Tradition, I guess. Turkey tends to get pretty old pretty quickly. I used to eat it once a week in the campus dining halls back in the 70s and I got so sick of it that I could barely stand it for a few years. Even then, I would still eat smoked turkey sandwiches.
Perhaps having Turkey twice a year -- Thanksgiving and Christmas -- is a way of spacing it out.
One thing that I'd like to try is goose. I've never eaten goose. I have looked online for goose and it was so expensive that I'm unlikely ever eat it unless I start raising geese (which I've seriously considered).
For some reason when I was a kid, we had baked red snapper for Thanksgiving and Christmas for a couple of years. Those were my favorite holiday meals ever.
I'd be perfectly happy for a good bowl of homemade chili with beans for Thanksgiving. Or a chicken fried steak with cream gravy, mashed potatoes, and field peas.