I first read the subject line in the same way as Javi.
I think there are plenty of terrible books written after movies. A fair amount of bad movies based on books, too. Some good movies.
Movies and books are different and tell their story differently. I think people don't keep it in mind enough. You can't just copy-paste from one to the other...
Also, I think movies are more of a match for short stories. It seems to me a lot of novels would work better as a series or miniseries. Obviously, that would cost more and bring in less money, so you can't be surprised it happens more rarely.