The Bible doesn’t say that Mary was sinless because the Bible is God’s Word and God cannot lie. If the Bible explicitly, or even implicitly, stated Mary was sinless then God Himself would be a liar. But the truth is God cannot lie, hence, the Bible cannot state that Mary was sinless. But instead it states:Rom. 3:23-24 "…for all sinned (Gr. hemarton, aroist tense) and (continually) fall short (present tense) of the glory of God, being justified (how?) as a gift (by what means?) by His grace (through what means?) through the redemption which is in Christ Jesus (the cross)"That passage is not stating that all “have” sinned, i.e., that all have personally committed sins, but that all humanity at a point in time, collectively, “sinned.”
So the fact that ALL humanity historically sinned is explicitly revealed to us in Rom. 3:23. When this historical event occurred is revealed to us in Rom. 5:12:“Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men (why?), because all sinned (aorist tense)…” The aorist is a statement of a past fact. “All sinned” (past fact) in Adam.
This is called “federal theology,” and the only way we can know of this fact is by divine revelation. God had to reveal it. It’s how God views humanity. Another example of it is in Heb. 7:9-10:"And, so to speak, through Abraham even Levi, who received tithes, paid tithes, for he was still in the loins of his father when Melchizedek met him."And so when Adam sinned Mary sinned, along with all of Adam’s posterity. It’s the reason the Bible cannot ever say that Mary was sinless. Long before Mary was born, nay, even conceived, she sinned with all of humanity “in Adam.” The only way Mary could have been separated from sin is to not have been connected to Adam at all. In other words, she would have to have been uniquely created by God - not born of human parents. And we know based on the Biblical genealogies that this was not true of Mary.
The only person ever born into this world apart from sin was Jesus Christ (Heb. 4:15). And Scripture reveals Him to be the “second man,” He Himself being another “Adam” (1 Cor. 15:45, 47). Not separately created but grafted on to the old through the virgin birth. He, like Adam, is a progenitor of another humanity, made righteous “in Him.” Paul, through divine insight, explains it this way:Rom 5:19 "For as through the one man’s disobedience the many were made sinners, even so through the obedience of the One the many will be made righteous."Paul’s sweeping statements in Rom. 3:23 and 5:12 should satisfy the O.P.'s question. It is impossible for the Bible to say that Mary was sinless, or support such doctrines as her immaculate conception and perpetual sinlessness without contradicting itself.
By definition the “oral tradition” of Catholicism is to find its origin in the teachings of the Apostles. But that which was preserved for us in holy writ proves that the Catholic “tradition” of Mary’s sinlessness was never an Apostolic teaching. And it becomes painfully obvious that those men who eventfully fabricated such a doctrine erred by not understanding the Scriptures and Pauline theology.