[@Archmage MC]: Because fights are still fights.

If everyone has no rules or limits and can just do anything, where does it end? I can't think of any setting like that with remotely serious fights, they all obey some kind of logic.

Even ridiculous stuff like Gurren Lagann or One Punch Man sticks to [i]some[/i] kind of rules, such as how Spiral Energy Works or different ways different heroes fight and what their enemies can do.

If there's no rules, it can so rapidly degenerate into "No, my character makes a shield that's better then anything yours can do!" and it removes everything that makes a fight interesting. It becomes an endless escalating mess of oneupmanship.

I don't understand what action anime you've seen, because [i]all[/i] of them have some kind of rules even to the vaguest extent.