1) Their company was in the Kakao circle-- scheming with various K-media online and offline outlets to denigrate other Kpop companies and the members of other Kpop companies that were not in their circle, etc etc.
2) Get awarded for middling quality in work, and not just weekly music awards but daesang awards (Not that I personally put too much stock on any award). "Love Dive" winning for various Song of the Year awards is bit much. So many are allowed to feel skeptical. (At least "Signal" by Twice didn't win this many Song of the Year awards, it knows its place and didn't overplay its hand, and only "pay" one or two patrons.)
3) The pre-debut pictures of various members were a genius piece of advertising, and many "fans" in K-pop bought it tooth-and-nail; and now they're lashing out because buyer's remorse has now turned to resentment because they now perceive that as false advertising.