Their reason to fight each other is because Luffy says so bruh, dont know what else to tell you
And how anyone can look at my PFP of Shanks' face and act like he also doesnt want to fight Luffy is beyond me.
This dude wiped and brutalized an ally of Luffy's in Wano (Kid and Killer are not antagonists), and intends to attack Bartolomeo. But sure, lets keep ignoring dialogue in the story.