There are countless examples of warriors who seek peace. The Jedi in Star Wars are established as warriors who keep the peace. Yoda outright says, "A Jedi uses the Force for knowledge and defense. Never attack." Aragorn, from Lord of the Rings, was a warrior. And literally the first thing he does when he's made king is make a speech about the importance of peace.
Why is it so strange for Wonder Woman? What makes her such an outlier?
The heart of it is absolutely writers who not only don't understand Wonder Woman, but won't engage with her as a character or her world or what Marston and creators that do understand are aiming for.
What most creators do when approaching a character is seek some core conflict or contradiction to build the story around. Spider-Man, for instance, has his conflict between his personal life as Peter Parker and his responsibilities as a hero. For Superman, many writers will run with the conflict of a god-like being trying to live among ordinary people. Wolverine, a man trying to be an honorable hero in spite of his killer instincts. And so on.
Wonder Woman has plenty of conflicts and contradictions that can be mined for story potential. But when you have guys who don't get her and/or are unwilling to engage with her, they latch onto the warrior/diplomat conflict because...it's easier? It seems like a juicy conflict? They don't know what else to do? Take your pick.
It's the same way they think making her Zeus' daughter is better than the molded from clay, powers from the gods origin. To them, the latter is weird and confusing, while the former is simpler and easier to get.
Azzarello even said, after they changed it, "We finally defined Wonder Woman."
I think a lot of it also stems from the stigma that Amazons = ancient people with swords and arrows and myth = Conan the Barbarian and Xena, therefore Amazons = warriors = violent brutes stuck in the past. Thus, when you're operating on such a narrow and shallow definition of what a warrior is, the idea such a character would seek peace seems contradictory.
It isn't, and it also completely misrepresents the Amazons and what they were intended to be by Marston, but that's what these writers roll with. It also, to them, makes Diana easier to write because it positions her as "the only good one" among the Amazons.
It comes from creators who aren't looking at Wonder Woman as an individual with her own world and lore, but as a small piece of some greater whole (the DC universe and/or the Justice League). The same way Superman is simplified to "boy scout" and Batman is "the smart loner" and Flash becomes "the funny, fast guy." Diana becomes "the warrior"...which doesn't mean anything, unless you decide "warrior" equals "Conan."