The reason behind that, I believe, is due to the fact that most OT fics follow the same plot formula of the anime. Those who have watched the anime since its beginning recognize quickly the same qualities between fic and show.
So those who like the anime read the fics and say that the fic follows the anime too closely. Those who hate the anime read the fic and find that the fic follows the anime, and furiously hit the back button. So views increase, but reviews don't, except from those vocal enough to complain/provide concrit.
I'm not saying that all OT fics follow the plot of the anime, even when written in the anime canon. (Mine is an example of this, though you can't see it.) It's just that the beginners who tend to give OT fics a try, and are "weak" writers, either follow the game canon too closely, or the anime canon. Since these fics are a dime a dozen, the general populace of forum goers hate OT fics. It's just another label the OT genre of Pokemon fiction has received. This stretches on to other fandoms as well.