I've played football (soccer for Americans) with people who were very good who didn't watch the game at all. Similarly for basketball.
People watch sports because it gives them an emotional investment in something that has a new result each week, is not scripted and shows incredible skill and fitness.
It's also a lot healthier than the people who follow politics like sport. They get moral when their team loses.
Do you watch TV, Internet videos, film, or read books ?
That's just another form of entertainment.