Robert says he's not playing the role, because the studio already said they don't want to use him. If they went and offered the role to him he'd jump on it in a heartbeat! He got $1,000,000.00 for playing Freddy in Jason vs. Freddy, and I think he got as much as $5 or $6 million in the Nightmare heydays.
He mostly does straight to DVD fare these days, so whenever he gets a chance for a big payday or reprise his role as Freddy he's in...
Personally I hope they use him, I just can't see anyone else playing Freddy and I personally think it might hurt the movie without him. Freddy is Roberts personality and without him is just a mistake.
Leatherface can be played by anyone, he wears a mask but Freddy... well Robert is Freddy. Not to mention Robert is just a great actor, who is grossly under utilized in Hollywood.