Because that's not how His Church was established. Some were appointed to be apostles, teachers, prophets, etc. Not all. He designated His Apostles and gave them the authority, and they designated their successors. He did not write a book for us and gave it out to everyone like the fish and the bread in a basket. He did not cause everyone to be able to read and understand. He did not say you will learn by reading, but by hearing the word of God.
There is no commission to make everyone a "pope."
The scripture was not completed until much later. The scripture was preached by word of mouth all along. And once it was written, not all of it was immediately recognized as scripture.
It was not a Jewish custom for anyone to read the scriputres. So, Christ, being a pious Jew, could not have taught otherwise.
Because not everything He taught is in the scriptures; even the scriptures tell us so.
Because people were illiterate and bibles were not cheap and affordable by most.
Many reasons, BD. All of which, biblical or historical, are ignored in defense of the so-called sola scriptura approach.
“He did not write a book for us and gave it out to everyone like the fish and the bread in a basket. He did not cause everyone to be able to read and understand. He did not say you will learn by reading, but by hearing the word of God.”
All that is necessary for salvation and life is contained in the scriptures and everyone, from the child able to read to the mature, can find the truth by themselves by the Holy Spirit in them. Everything else is just opinion and commentary. Liturgy can’t save, desert fathers can’t save, hermits can’t save, councils can’t save, churches can’t save, Pastors/Priests/Bishops/Patriarchs/Teachers can’t save, good works can’t save, parents can’t save, baptism can’t save, circumcision can’t save.
From the Apostle John:
John 20:30-31, “And many other signs truly did Jesus in the presence of his disciples, which are not written in this book: But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.”
1 John 2:26-27, “ These things have I written unto you concerning them that seduce you. But the anointing which ye have received of him abideth in you, and ye need not that any man teach you: but as the same anointing teacheth you of all things, and is truth, and is no lie, and even as it hath taught you, ye shall abide in him.”
From the Apostle Peter:
2 Peter 1:19-21, “We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts: Knowing this first, that no prophecy of the scripture is of any private interpretation. For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.”
From the Apostle Paul:
2 Tim. 3:16-17, “All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, throughly furnished unto all good work.”
From the Apostle and brother of Jesus, James:
James 1:25, “But whoso looketh into the perfect law of liberty, and continueth therein, he being not a forgetful hearer, but a doer of the work, this man shall be blessed in his deed.”