Because there is all the difference in the world from what God says is a blessing, as in having a child, and what the Catholic does in their "veneration" of Mary. There is no "veneration" of Mary in the bible. When He says "more blessed" He redirects that person from saying Mary is blessed to the fact that any Christian is more blessed for simple faith than Mary is for being the "Mother of God". This is like when He said John is the greatest of women born of men but any Christian is better than him.
He doesn't. Read the Bible every once in a while with attention and you, too, will be Catholic like me and understand the Holy Scripture.