Why did Shaman Tanks get removed?

I don't play a Shaman and PvE was never my prefered side so this doesn't actually effect me. I'm just curious though cause in BC and LK there were some damn good one's.

Even when they added LFG in LK...way before Class/Roll restrictions, it seemed like I got more Ele's than anything. They had great AoE and could hold aggro well. Plus they had decent survive back when gear type meant a bit more. I've just never been able to wrap my mind around why Blizzard didn't want them in that roll.

Obviously nobody cares about it anymore and it does nothing but get Lock Tank conversations started, but still...