Why do some people (who aren't from NYC) root for the Yankees and others the Red Sox? Why don't people change favorite teams every few days or weeks?
When I played Little League ball the team assignments were essentially random. There was no real difference between the teams, at least not any more than the variety among players on any one team. Any kid could have played for any of the teams and nothing much would have been different. Still, everyone was expected to be loyal to his own team and to fight hard at all times for that team to beat the others. Anyone who didn't was looked on with contempt. Why? Because team loyalty is one form of sportsmanship. Even at the age of eight that wasn't hard to understand. And it made league play more fun and more intense than pick-up games.
School teams aren't that different. Are the students at State really all that different from those at Tech? Are the players? Aren't the players at both schools more like each other than any of them is like the general student body or the fans? But we still have loyalty for our own school.
One reason I've lost interest in the NFL is the players move around way too much. You don't know who half the guys are, you don't know who you're supposed to be rooting for this year or next. There's no continuity, no loyalty. The coaches change way too often as well. And the teams themselves move too often too. No loyalty by anyone. Why should I cheer for a bunch of random guys I've never heard of, or half of whom I cheered against last season?
How many people here were in the military? Didn't you have pride in your own unit? The guys in the other units are all on the same side too, they're really no different from you, but you want your unit to excel, to be the best. Then you're transferred to another unit and you want that one to be the best. That competition, that sense of pride, are a large part of what drives excellence. Would any units be as good if they randomly reshuffled personnel every day or two?
Tribalism is human nature. When it comes to teams in games it's harmless, even beneficial if it makes people play harder and enjoy the game more. it only becomes harmful when people start to hate those on the other side(s) or associate membership on one team or another with moral superiority. The stakes are much lower in Aces High than they are in the military or even in college football, but the basic principle at work is the same. You fight for the team you're on. You may change teams at some point. When you do, you fight for that team. And you take pride in your team.
If you play enough you will come to know the people on your side better. It becomes fun to fly with the same people, especially if you're in a squad and even more so if you have other squads you like to work with. It isn't loyalty to "a chess piece" any more than it was loyalty to a team color or mascot in Little League, it was and is loyalty to your teammates - not because they are different in nature from those on the other teams, but just because they're your teammates.