[donavannj]

Because prerelease Raichu is far more known, therefore far more sought after, than the Mewtwo movie promo that has the Pokemon movie logo printed upside down. People are more wary about the misprint Mewtwo being a fake, as it seems to be a fairly recent discovery compared to prerelease Raichu.

EDIT: Oh, and also some artificial price inflation on the part of those who sell the prerelease Raichu cards. Many have gone and posted it for more than it sold for when it was previously listed.