just because it is a movie, and people like to see the beauty of fights. if all goes at once, there will be no beauty, it will be mess, and the hero will have no other choice than run the hell out of there sight. it will be a flop movie.
simply, as it is a movie.
Dude. It's a movie. It doesn't have to be real. The good guy wins because he's the good guy. They can even make the good guy fight 1 million super ninja with a rubber umbrella.
Because it would be a very boring and short movie.
So, if you've watched any martial arts movie you probably already noticed this but haven't thought much of it.. but this bothers me a lot. Theres always this one invincible martial arts dude fighting like 50 people and he still manages to take them out right? But the bad guys always enter 1 at a time or 2 at a time. 1 bad guy goes in and gets knocked out then another goes in. Why don't they all go in at once? Then they can overwhelm the good guy. But instead they wait and watch in the background moving around watching their fellow bad guys get kicked in the face or something.