I think they started signing them up early after Crispin Glover asked for too much to appear in Back to the Future 2. They used a lookalike and he sued them successfully, then went on to kick David Letterman in the head wearing big platform shoes and a wig.
Is it like how Drew Barrymore wasn�t in Poison Ivy 2 and she went on flash her b**bs at Dave Letterman?
Hmmm... coincidence?
Methinks not!