Why does splitting territories fairly still turn into politics?

You already did the hard part. You built a map that is fair to the whole team, not just to the loudest voice. And still — the arguing continues. You think the problem is the map. It is not. The politics you are tired of was never about the numbers. It is about who feels they lost, and about your own wish to be liked by people whose job is sometimes to lose. No design removes that. No spreadsheet makes someone feel chosen last and not mind it. So ask what is actually yours to control. Not their feelings. Not their opinion of you. Only this: did you decide clearly, for reasons you can say out loud, and will you hold to it when they push? Choose that, and stop waiting for a consensus that was never coming.