The U.S is a very aggressive culture in terms of culture and they channel it into sports. People are extremely addicted to watching sports as well. Its very strange for Americans to sacrifice all their time and energy in watching sports. For an example over 70% of the population watches the super bowl.
People also place bets on sports. Some Americans, men in particular, bet all their savings on sports game. They're aggressive when they watch them, because they are afraid of losing their earnings. People won over millions of earnings from the Mayweather vs. McGregor fight alone. The U.S has a very aggressive culture in terms of culture and they channel it into sports