Easy: because that is what people want to see. Nobody wants to view a boring show. If they can show an antagonist/protagonist struggle, the audience is more captivated. It also allows one to see conflict resolution (or not).
Anyone who has a true passion for something usually can pinpoint when that started for him or her. For me, it began when I was a young boy, watching the sole black and white TV in our house, complete with rabbit ears for reception control and a mere three or four channels. My Dad worked long hours and my Mom discovered frozen TV dinners. I used to love eating those things,