Here are my humble theories on why he does what he does.
a) Ruining the character of Darth Vader to further piss off David Prowse (and replacing every Prowse/Vader photograph with Christensen/Vader material, so Prowse gets as few royalties out of that stuff as possible).
b) He seriously believes the world is gonna end in 2012 and wants to help us to be glad it's finally over... D;