Yeah but originally, pre-merger it was just East and West in the NFL and they were in the East while Baltimore was in the West. My guess is either they wanted to be in the East for the exposure (remember, they were an expansion team in 1960) or maybe the league wanted them there to help them get the exposure. Those rivalries weren't like Eagles-Giants or Bears-Packers, going back to the beginning of the NFL, they only exist because the league put Dallas in the East in the first place. I believe they also lobbied the league to get the 2nd T-Day game every year where before it was just Detroit hosting one game and the other game was any other two random teams.