Because the Roman Catholic Church is a blending of the occult,paganism,and Christianity,like Joseph Smith,the Mormon Church, is a blending of what he believed with Christianity,like L. Ron Hubbard,Scientology,is a blending of what he believed with Christianity,and so forth,which what they believe that is not part of the Bible,is the foundation for the interpretation of scriptures.
All have sinned and come short of the glory of God,so that would have to include Mary,which Mary said she rejoiced in God her Savior.
There is only one person that the Bible says received the Spirit from the womb,and that was John,which did not save him,but gave him power to strengthen him to prepare the way for Jesus who was to come in the future.
The Bible does not say that Mary received the Spirit from the womb,nor does it say that Mary was not born in to sin,which Jesus said that those born of women there has not been a greater than John the Baptist.