WoW Logic: Infallible ~_~Attack animations would be why they won't let people transmog stuff to look like polearms. I guess they apparently don't have the tech to just say "oh, it's transmogged to a polearm? Use polearm animations!"
The reason there aren't any strength polearms now is because they're pretty much reserved for agility classes, namely druids and monks. Used to be hunters too before they got to wield ranged as the main weapons. If they were to add a strength polearm it'd cause some loot problems, or at least that's what they claim. Funny how they're reserving them for the four agi specs that can use them, but five strength specs could use them instead if they were strength.
I'm glad I quit that game