Why is conflict at the heart of all fiction stories?

Because conflict makes a story interesting. Nobody wants to hear a boring story about how somebody went to the store and bought tomatoes because that's an every day thing you don't need to hear about this because chances are you have done it. So authors use conflict to keep you on the edge of your seat. Some are better at this than others. There are different types of conflict man vs man man vs nature man v self man vs society. But these conflicts are the basis for almost every interesting story written