The question of where boxing originated from and why we are fascinated by it is an old age question that has a simple answer. As humans, we enjoy violence. Other than our hands, we have our legs and elbows as tools, along with grappling, hence the birth of MMA.
There wasn’t anything more manly than striking each other with just fists, as upper body ability has always been admired by the general populace. First it started as something to settle feuds between men, and then it became a sport to see who is the most physically proficient and the toughest.