I have inherent bias that dictates my rooting. There's certain teams/conferences I root for or against (love to see SEC teams lose, Ohio State should always lose, PAC-12 can lose too for all I care, grew up in B10 country so root for them except previously mentioned OSU, oh and Memphis) etc. Other times it's more subtle, like I'm more familiar with certain teams or aspects that I root for or against. Sometimes if the game is very obscure I just like seeing the home team win for the fans, since I hate attending a loss.

It's harder to explain to your 6 year old why you want the white team to beat the red team, but that's for another time.

It's the same for almost every sport - generally cheer for NFC over AFC, NL over AL, etc.