The Guardian interviewed Philip Pullman, one of the three "leading children's authors" in the UK at the moment—a man whose dark and noncondescending work greatly transcends anything in Barrie's fluff.
Philip Pullman, whose His Dark Materials trilogy was voted third most favourite story in last year's BBC Big Read poll, said: "I wish Great Ormond Street very well, but I can't help feeling that they've got the process the wrong way round. It wasn't Great Ormond Street that thought up Peter Pan in the first place, and then went to Barrie and commissioned him to write the play. It was Barrie who wrote it, out of the pressures and fascinations and obsessions that attend any literary inspiration, and then gave it to them. That's the only way literary masterpieces come into being. I just can't see how the process could work the other way round."
John Ezard, "Hospital Challenges Writers to Make Peter Pan Fly Again" (20 Aug 2004) (fake paragraphing removed for clarity). This is certainly a valid-enough reason to beg off; but buried a little earlier in the article is the most important reason to reject this "opportunity":
The hospital would hold copyright, including crucial film rights, in the sequel, but would split publisher's royalties with the author. Its lawyers said the author "could reasonably expect to participate in the exploitation of film rights."
(emphasis added) "Participate," huh? Monkey points, I betcha. And note, too, that the contemplated split is not disclosed.