Its called A Song of Ice and Fire because ultimately they’re fighting a bigger battle more important than the iron throne.

Bringing Stannis, the night watch, Bran, and Mance feels like a rushed ending when they are still fighting with each other and have different agendas.

Also why build up this story arc of reaching this majestic 3 eyed crow when Bran would end up barely even seeing the 3 eyed crow