The world has Social Darwinist standards and has tough living conditions, which forces people to be an Action Survivor at least. This is the method a large majority of societies in order to breed powerful human beings for their success.
Enforced: The writer or executive wants the show to have a lot of cool fight scenes to draw in new viewers.
Lampshaded: "You, my friend, are a Worthy Opponent just like everyone else I know. You're nothing special."
Invoked: The world has adopted Social Darwinist standards just so they can live such a world and will be safe if there any alien invaders.
Exploited: Alex Cunningham the lone-wolf wants to hire someone to guard his stuff while he's gone and wants someone tough & trustworthy. Aware of this trope, he chooses random people off the street & makes sure that he can trust them before telling them to guard his stuff.
Discussed: "Why does everyone have to so badass? I mean god could have, at least, made one of my enemies into a wimp. Good thing I'm not one though."
Conversed: "Why would they make everyone start out as a badass? If you think about it, it'd more impressive for a wimpy character to learn to accomplish such feats and become badass over the course of the story."