Further to Christopher's point, Hollywood in general seems more prone to choosing the lethal option. Most of the Trek films, for example, end with the heroes causing the villain's death. Why this should be I don't really know, other than a surmise it's born of similar logic to sex so often being used as a shorthand for intimate relationships. It's an easy way to narrative catharsis, the villain getting what they deserve, the romantic tension resolved. Problem is, at least in my opinion, it's too often not a satisfying approach, because it isn't properly earned. Or, in the case of Superman killing, goes so strongly against the popular perception of the character.
And I agree with Awesome Possum that everything happens in a story because the teller wants it to. The trick is not making the artifice obvious, and thus not undermining your character, emotional, thematic intent. It needs to feel like a natural development, with build-up and consequences, and that's really hard to do, especially if it's heavy, dark stuff like the "awful choice" trope that seems so prevalent at the moment. You do it wrong, it just feels like you're being grim for the sake of it, a trap that, for me, so many keep falling into, including Zack Snyder.
I can only hope James Gunn can avoid it.
