Sometimes people will hate something simply because its become too popular, they'll focus on their flaws and downplay the elements the anime gets right. When we enjoy something we talk about it and what we say set the expectations of other people. Death Note, Naruto, One Piece are such kind of anime that people might have tried them with a distorted idea of what to expect due to all the praise, and the bitter disappointment can be a reason why they flip against it and the people liking them, as they can't understand why is it seen with such a high regard or if they see why, they still consider that the anime doesn't deserve it.