Too many people do the riffle pass because the riffle covers an inadequate pass. They can almost do the classic well enough - so just in case, they perform the riffle, which is obviously a flawed way of thinking. I think that in order to perform the riffle pass correctly, one must first have an undetectable classic pass - the riffle is used as an added layer of subterfuge to an already secret move, not to cover an imperfect one.