I wonder how much of that is due to culture and how much is simply due to habit. The only person Clark routinely interacts with who's more powerful than him is Mxy, and even Mxy, Clark could probably just fry with his heatvision if he were so inclined (Emoboy certainly didn't have any trouble hurting him). Even Bruce, despite being a badass normal, has never fought anything he can't defeat - he has no rogue he can't either outsmart or outfight or usually both, he's heavily inclined toward Batgoddery on the Justice League, he always has access to resources (Mother Box, other more powerful Leaguers, etc) that can make up the difference. Neither of them kills, but they nevertheless operate very much in that mode; their victories rely on their opponents being killable. Beating someone until they give up is a difference in scale, not kind, after all, and thus if you set them against a god, they scale up and go for the kill as usual.
Diana, on the other hand, was fighting Ares right out of the gate, and her most regular rogue outside Cheetah is Circe. Further, her primary goal on this Earth is to end war and prejudice. She spends every single day wrestling with an opponent that no amount of punching or clever analysis will ever make the least dent in. She's not even playing the same game as them, and her default understanding of victory doesn't involve the hurt-maim-kill MO. So she's not going to make the mistake of using that MO where it isn't applicable.