Gladiatorial bloodsport is pretty much human nature and it's far healthier to fight with rules than without. If it's two consensual fighters, there's no problem.

Plus, human life is so bland, boring, banal really. People crave escapism, they instinctively crave fantastical conflicts and magical powers and to be a hero because of how unnatural and bland our lives have gotten as a whole.

This lets people who view and who fight spice their lives up directly and experience those feelings.