Precisely why Yeshua banned all oral tradition.
An excellent cartoon.
Jesus' criticism of the Scribes and Pharisees in Mark 7:13, "that you have invalidated the word of God by your tradition," is not a blanket condemnation of all tradition, but rather, a correction regarding a particular tradition of man (the Corban), a bad tradition that had circumvented a commandment in Scripture. According to this tradition, a son could declare that what he had intended to give his parents was considered "Corban" (ie. a gift devoted to God). Once a gift was considered "Corban" it could technically (though not actually) be no longer available for the care of his parents. Wouldn't you condemn a tradition like that?
From Adam and Eve to Moses (1400 BC), oral tradition was the only means of passing on the Word of God. And from Moses to the birth of the Catholic Church on the day of Pentecost, it was clearly understood by all in God's covenant family that the "Word of God" was made up of Tradition that was handed down both orally and in writing. St. Paul exhorted us to "stand firm and hold fast to the traditions that you were taught, either by an oral statement or by a letter of ours" (2 Thess. 2:15).
Rabbi Hayim Donin in his book entitled To Be A Jew explains that "we believe that God's will was also made manifest in the Oral Tradition or Oral Torah which also had its source at Sinai, revealed to Moses and then orally taught by him to the religious heads of Israel. The Written Torah itself alludes to such oral instructions. This Oral Torah which clarifies and provides the details for many of the commandments contained in the Written Torah was transmitted from generation to generation until finally recorded in the second century to become the cornerstone upon which the Talmud was built" (p.24-25).