Why are NFL fans so boring?

Okay, don't get offended... but here is my point. Americans claim that American Football is the greatest sport in the world. That's your opinion and I will not judge it. But why are the Fans in NFL stadiums so boring if the game is supposedly exciting? I've been to Cowboys, Raiders, Redskins and Chargers games games so far. What I saw was disappointing. There is no comparison to soccer fans around the world. Don't fight me for my opinion. If the atmosphere in a German or English soccer stadium is at 100, the NFL stadiums barely reach a 20. So what makes it a great sport to watch if people in the stadium just sit on their s and eat nachos?