My guess? He saw a sketch of the make-up he was going to have to wear and fled the building.
No, apparently it's down to "scheduling conflicts", and here's the kicker: the scheduling conflict in question is the upcoming adaptation of John Milton's Paradise Lost, which is being helmed by the director of the original Crow movie, Alex Proyas. Is it coincidence, or something more? Proyas has been down on the remake of his film from the very beginning. In an interview with DigitalSpy.com, he had this to say:
"I have nothing to do with the remake of The Crow. That's other people involved with that and I wouldn't even dream of remaking the movie, because as far as I'm concerned that's Brandon Lee's movie and that's why I finished the movie – in memory of Brandon. That's the only reason I finished it actually.
"So the whole notion of remaking it, to me, is just ridiculous and I'd have nothing to do with it, as I've had nothing to do with any of the sequels or the TV show or any of that stuff."
Make of that what you will. I'm not saying that Proyas badmouthed the remake enough to make Cooper back out of it, but in the ongoing Hollywood soap opera in my head that's exactly what happened, and there was screaming and someone got slapped, and then a glass of water got thrown in someone's face.
Current possible replacements for Cooper include Channing Tatum and Marky Mark Wahlberg of Marky Mark and the Funky Bunch. Fingers crossed for Marky Mark, I would dearly love to see him in Brandon Lee's goth get-up.