When I worked for an ad agency, I would meander up the street to Beefy King. Black Friday was one of their busiest days. At lunch, I would go there to help out. One of the most popular sandwiches that day was turkey breast. For the life of us, the owner and I could not figure out why turkey would be such a big hit the day after Thanksgiving. You'd think people would be tired of it by then after eating so much the day before, or, they would have enough leftovers that they wouldn't want it from a restaurant. Nope, they ordered it big time.
Roland and I went back and forth, over and over again, trying to understand why people would want turkey. We went a couple of years thinking about it.
Finally, it dawned on us. We figured these were people who had to work Thanksgiving Day. The ones who took your gas money at convenience stores. The wait people at restaurants who served dinners that day. Bartenders. Maybe some car dealerships were open. They were shortchanged on Thanksgiving and were just fulfilling their cravings for what they did not get to eat. Maybe some people ate ham instead, yet they still missed the traditional meal. They needed that turkey fix.
That's the only reason we could think of.