Because, especially in her pre-tripleGut stage, she could 1shot people from passive AA on-hit alone. She could miss every spell and still 1shot people.
She has not 1, not 2, but THREE abilities that are either overtuned, impossible to balance, or both due to their design, especially when they are combined and used together. W is basicaly Kleptomancy on 10 steroids; the Q is old Nid's Q on steroid especially when used with her "ultimate" that has nonexistent CD; and E is the most disgustingly overloaded spell in the entire game and on a basic ability slot, especially the kind of utter madness it was when it was first released where it was basically 2 ulties on a basic ability that could also refreshes ON HIT (not even have the decency of on-kill, no, ON HIT. What the?).
She also has a very weird power budgeting, it's almost as if they basically took and power budget of ulti and simply distribute it in her normal spells; and pretend as if because ulti has low budget it means the normal spells can be overpowered as fuck. Mate, that's not how the game works, why is this design even green-lit? And worse, not only is the power budget of ulti spread across the normal spell, what they actually went for is that each single normal spell has at the very least, the power budget of an ulti (as mentioned, something like E used to have at least the power budget of 2 ulties).
Ofc she's going to be hated. She is easily the most broken champion released in the entirety of League's history and probably ever will until CertainlyT flexes his """"creativity"""" again; released as being both massively overtuned as well as having the most amount of clearly unbalanceable design issues.
