God loves the spoken word as well as the remembered word. What better way for the spoken word to be remembered AND followed for the rest of time than the written word? It obviously took some time before mankind figured out HOW to write the spoken words, but God had a hand in that, too. There is no better method of preserving exactly what God said than the written word. We have the sacred Scriptures because GOD intended us to have them. Man cannot claim the credit for that either.
With the written word, someone can always go back and verify what was said.
With oral tradition, there is simply NO WAY to verify that what was passed down has been passed down faithfully.
The claim that it's been supernaturally protected is desperation to an astounding degree.