thats because when i started in wow my rotation was frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt, frostbolt
you get the point, there wasnt much calculating to be done to be better, when you have 10+ abilities that have a potential to be part of a rotation you need something to find the optimal order and priority of these abilities.