It's more about aesthetics and flavour. No one is denying that pandaren were canon but they (from what I heard) were kind of like a joke never meant to be added to WoW. Up to cataclysm we have a western mythology mmorpg with dragons and all. It fits, it's a nice overall feel. But in mop... They mixed Eastern and western mythology and the aesthetic was ruined. It became tasteless and weird. It's like adding to much and unnecessary ingredients to a dish to the point it becomes disgusting. Or when you take a cool car with a nice colour scheme that makes sense and ruin it like a ricer by adding a useless spoiler, lower it too much that it looks ugly and paint it shit colours. I know it sounds weird but it's the best way to describe it.