In 1966, the team wasn't all that good, but Schramm saw an opportunity to gain national attention with a Thanksgiving game. The NFL wasn't sure it would work. It gave the team a revenue guarantee in case no one showed up. It wound up not being an issue.
The game was played in front of a record-setting 80,259 fans. The success of that game set up a second NFL Thanksgiving tradition, which, since Reba McEntire in 1997, has included a halftime concert. Only twice since '66 have the Cowboys not been in action on Thanksgiving.
The addition of a third Thanksgiving game wasn't much of an experiment. It's clearly big business for the NFL. In 2006, the League began wondering how Americans could possibly survive with only six hours of Thanksgiving football. To save people from the drudgery of talking to family, it added a third T-Day game, played at night after the Lions and Cowboys games conclude. No single team has a stranglehold on that slot, however. Two different teams are featured each year, allowing fans everywhere the opportunity to experience holiday disappointment in their hometown team.