I just read an interview with Jurassic Park and Spider-Man writer David Koepp.
The interviewer asked why everyone thinks they are qualified to change screenwriting:
William Goldman said once that it’s because everybody knows the alphabet, so everybody thinks they can write. And, by extension, everybody thinks they can change a writer because, basically, anybody can write. And it’s the cheapest, easiest part of the production to change. You can even have more than one [writer] going at once, which isn’t the case with a DP or an actor or anybody else. The majority of the other jobs involve a tremendous amount of upheaval because the majority of the other jobs on a movie don’t start until production. But because the writer works in the netherworld of development, where time can expand infinitely, there is much less risk and turmoil in changing writers. And you can always go back to what you had. It’s the hell of too many choices.
Does any of that sound familiar from your own line of work?
UPDATE: here’s another excellent article on the subject (thanks, S).