Thank you for the question on Scripture, “Why do you think that the scripture does not include the New Testament?”
If I may venture an answer to the question that may help clarify one’s question:
The term Scriptures refers primarily to the Old Testaments. One must remember the early Christians only had the Old Testament and the words of Jesus.
Jesus said this in Luke 24, “He said to them, “How foolish you are, and how slow to believe all that the prophets have spoken! 26 Did not the Messiah have to suffer these things and then enter his glory?” 27 And beginning with Moses and all the Prophets, he explained to them what was said in all the Scriptures concerning himself” (NIV).
The Apostles were living witnesses through the enablement of the Holy Spirit to recall all that Jesus spoke to them. The spreading of Jesus’ words expanded beyond Jerusalem, Judea, Samaria into Asia Minor and even into Rome by the Apostles and by those who heard and believed the message of Jesus.
The words of Jesus were later written down by the Apostles or those closely associated with them and the teachings of Jesus were expanded by the Apostles including Paul. The letters of the New Testament were written to various people group or to churches who need guidance in following the words of Jesus. Those books or letters were treasured by the early Christians which became the canon for the Christians.
The Jews accept only the Scriptures of the writings while Christians accept the Scriptures of the Jewish writings and the writings of the Apostles.
One further thought for one’s consideration is that even in the writings of the prophet their words may not have been readily accepted by the religious leaders or even by the kings of Israel. It is only in time that those writings were collected and accepted as the words of God through the prophets.
The Book of Isaiah, Jeremiah, and even Ezekiel as it was being proclaimed didn’t find favor with the kings or the religious leaders. The prophets were condemned as heretics and discouraging the people of Israel. King Jehoiakim in Jeremiah 36 is recorded as cutting the pages and burning the scroll that Jeremiah wrote as he head it. God told Jeremiah to rewrite it.
In other words, there was a process in which writings of the prophets and or the Apostles were recognized as being from God. That is the subject of canonicity that one can read if one wishes to research that topic more.
SUMMARY: The Jews rejected Jesus and his teachings as heresy along with any of his followers and their writings. Thus the Jews do not considered the writings of the New Testament as Scriptures but false teaching.