@Sally - okay, I'd just like to clear this up, because it drives me crazy when I see it.
Authors do not have veto power on the movie adaptions of their books.
None. Nada. Nil.
Once they have sold the rights to a film company, that's it - the film company has the rights to the name and characters, and nobody else can make a movie with them. They're allowed to do whatever they want with those rights, including making a movie that shares nothing with the book it was based on.
The author does not have ANY official say in what goes into the movie. Once they've sold the rights, they have no power over the movie. Yes, they may have unofficial power, but the film company is perfectly allowed to just ignore them.
And unless the film company sells the rights back to the author, the author can't even go sell the rights to a different company, who will be more faithful to the book. Rick Riordan has tried to buy the movie rights back for Percy Jackson, but he has so far been unsuccessful.
So really, it's not that the author let them do anything. The author has no say in the matter.
There was at least one notable exception - and that's JK Rowling and Fantastic Beasts & Where to Find Them. JKR had veto rights there - but that made headline news, as it was completely unprecedented.
So please, don't blame the author for allowing an awful adaption of the books, because they have no say in the matter.