The same psychology that drives idiot parents to yell, spit, punch, swear, etc. etc. etc. at youth sports everywhere. It transcends economic class, race, education level, you name it. The psychology is simple: a lot of people are terrible fucking morons who only take up space and contribute nothing of substance to the world. And these people are likely to procreate and force their children into sports whether they want to be there or not.
If you want to absolutely hate humanity, go ump little league games for a season or two. I couldn't have been happier when my son decided he was done with baseball so we could get the hell away from those people.
Any adult who actually cares about the outcome of a youth sporting event to the point they have a visceral emotional reaction, whether it's a tee-ball game or a high school football game, should either seek professional help or do the rest of us a favor and disappear from society. Yelling at a youth sporting event is like holding up a flashing neon sign that says, "I'm an emotional toddler trapped in a grown up body and present a very real threat to those around me. It all stems from the fact my dad never really loved me and didn't care that I knew it. Also - my own kids hate my guts but I'm too stupid to see it." (EDIT TO ADD: It's a big sign.)