There's a huge difference between "I didn't like X, Y, and Z" and constructive criticism. Maybe I didn't like the story because it didn't have flying ponies. Maybe I hated the top/bottom situation. Maybe the writing was too flowery, and I can't be arsed to explain what I mean by "too flower" or pull out examples.

Disliking authorial choices =/= constructive criticism. It's just dislike. And saying something was bad doesn't make that a constructive statement, even if it's true.