because she sucks balls mid lol
325 movement speed while Emperor Balanced (aka Azir) got 335 while having higher HP, armor, and a dash + shield and Xerath got 340 while having a faster and longer stun and way higher range: #logic
lowest base HP in the game
E is too much slow and roots for only 0.75 at level 1 so it's best used on 2 people (aka as support)
Plant AI bugged as heck
Shitty passive
she sucks balls even @ support after the nerfs (and that's the reason why you don't see her in LCS or any other league since 3000 B.C.), but if you master her you can manage to have a decent winrate, so i guess to Rito's balance team this is all that matters
P.S. her scaling sucks, W plants got 0.2 AP ratio