Because Jehovah's Witnesses take the beliefs of Christianity and twist them beyond recognition to their own purposes; and because they take the Bible and rewrite it so it will promote false doctrines; and because they say they are the only true denomination and deny that Jesus has any part to play in all of Christendom; and because they have absolutely no idea who Jesus is; the Catholic Church considers the Jehovah's Witnesses apostate and does not recognize them as Christian.
I wonder how JWs would react if you called them apostates to their faces next time they came to your door?
StAnn