Well, now he has. So why the sudden change of heart? Basically, Argento is convinced that his original is a masterpiece and that since it will never be overshadowed there's no harm in letting someone else try. Can't say I disagree with the logic.
Morabito also took the time to dispel the rumor that Marilyn Manson had been selected for a supporting role: "No, it's just a rumor. I read it too on the internet and I don't know where it comes from! We never even thought about that."