It's a bandwagon, to be sure - almost every hate train is (NOT NIDALEE, EVERY OUNCE OF NIDALEE HATE IS 100% VALID ARRRGH) - but Kalista is still frustrating to play against, and frequently frustrating to be tied to. Her hopping gives her a significant amount of extra defense against skillshots, the most prevalent form of poke in the game, and she gets this defense without even having to put forth much effort. She gets a lot of unusual tricks without having to pay for them, and while she doesn't have Vayne's dueling or Draven's raw damage, Kalista still gets a TON of ADC perks that don't require much skill expression.
She's a pain in the ass to lane against and she has enough quirks that she can function lategame without necessarily having to rush Infinity Edge like everyone else.
I'm not calling for her to be deleted or nerfed to oblivion, but there will always be people who hate her simply because of how her kit works.