Accidently unlikable characters.

You know, there are characters we should hate, like Baron Vladimir from Dune, there are those who evoke double feelings, like Eric from The Phantom of the Opera, and there are those for whom we should root and empathize, but the author accidentally makes them unpleasant. These include most of the characters from YA, such as Grim from Lightlark, who combines the worst of the "dark sexy handsome manipulator" or Lila from Shades of Magic, which is one of the reasons why people DNF this series.

And I always have a question: How did the author not see this? Like, V.E. Schwab didn't see what she was making of a cheeky girl, a sociopath around whom everyone was "wrong" and only she was "right" in everything and at the same time she was the best? Why is this happening at all?