Because , shes mostly about her E Shield. She`s way too squisy to tank or to be a frontline,
U can`t just nerf a champion without a good reason. She is in a good spot atm , with defined weaknesses. Long cooldowns, with high mana costs. But, u build her with 45% (that is what i do at least), and buy a lot of mana regen items.
Take Lulu for exmaple: Q - Slow / Damage | | | W - AS / Polymorph | | | E - Shield / Damage. She dosen`t have to put herself in danger.
Lulu, can neutralize with her W high priority targets, slow them with her Q , shielding an ally, and in case it`s needed ult an ally for more HP.
Janna. Q - Knockup+damage | | | W - Slow+damage | | | E - Shield+Ad. The damage it`s not even there, so im going just to put that in case some1 will complain about it.
Janna, has to hit her Q , in order to do something , when her Q its only good when it`s half/fully charged. Her W can put her in danger, but also slows an enemy. Only 1, not like lulu slow, that if well placed, can slow up to 2-3 persons, or even more. Shield an ally, and can ult and heal evry1 around her for 3 seconds. Shes vulnerable during that time, if not well placed.
(Tho, Janna it`s getting some changes, so i expect them to be quite good, and make her even more useful.