New York Giants / Jets comes to mind as well. On top of that, there are other competitive factors involved, e.g., in Baltimore, the Orioles and Ravens generall

New York Giants / Jets comes to mind as well. On top of that, there are other competitive factors involved, e.g., in Baltimore, the Orioles and Ravens generally can't be playing mass-attendance games at the same time because they are too close together, and share parking infrastructure. That of course has to be scheduled around. Beyond that, there's the rather mundane reality that stadiums aren't just used for sports. Even during football season, megastars like Beyonce and the Rolling Stones need venues to play in. And of course, stadiums are loaned / leased out for a panoply of other reasons as well.