Sion Jungle, the ignorance of a powerhouse

My main question is why Sion isn't as popular for his godly jungle, I have been playing him in the jungle since before his rework and after season 4 it just got rediculous. His ganks pre 6 is definitely weaker than post 6, but pre 6 he can still coordinate his laner's CC so that the opponent has to watch him slam his axe in their face for the knockup, post 6 he just ults down the lane and you pray to God he isn't coming for your lane, and then you realize he wasn't coming from his side and you have a battering corpse coming from your side after he just stole your ally's camps with minimal effort. And then his clearing, 3 AoE abilities that Raptors don't even phase him during the first clear, his sustain just makes it more rediculous that either he kills the lesser creeps fast enough that the big ones are alone with the shielded Goliath or his Sheild is able to soak enough from the smaller monsters that he takes minimal damage. And then all those creeps fueling Soul Furnace is even more once you realize how great it stacks with Cinderhulk, making it easy to get 4k health and still have respectable armor and MR. On the off chance he falls behind late game his use as a meat sheild and his initiation power combined with respectable base damages and %health AoE means he doesn't actually fall behind and can still be a threat that can carry through his power. Now his build is pretty basic, Cinderhulk, boots, Titanic, and then whatever tank items you need, special mention goes to Warmogs for a massive amount of regen between fights and CDR, Spirit Visage to add to both of these, Randy's Omen and DMP for chasing down those people that realize they can't chew through you fast enough to live through you, your team, and your hydra

TL:DR Sion is a heavy damage tanky option like Vi or Lee Sin that can't fall behind as easy so why doesn't he see jungle play