For RP/customisation reasons, they should aim to give weapon diversity to all classes where it doesnt clash with the fantasy/theme. Paladins and survival hunters should, as well as blood and unholy dk should be able to dual wield. And enhancement shaman should be able to wield two handed weapons.
I also find it curious how spears have been cast aside for most of wow’s history, and how even today it is only relegated to survival hunters. I means spears where the go to weapon for most of humanities history. I find it funny there still is no class that can wield a spear and a shield in this game.
My theory for why spears are casted aside in this game is that it is because of the fact that they are wielded in a radically different way compared to other two handed weapons, they are trusted instead of swung, and Blizzard didnt want to make specific animations for them when all the other weapons could have the same animation.