Easy ! The NT boox were all written by an apostle, fit together readily, & have been in constant use from the time they were written.
That is incorrect. Mark and Luke were not Apostles. As for the other Gospels, "
The Gospel According to John" is not part of the original manuscript. It was added by the Church
based on the tradition of the Church.
The Apocrypha are somewhat different from the canonical boox & have not been in constant use since ancient times.
Can you please tell us why you believe they belong in the canon ?
You are incorrect again. The Deuterocanonical books ("Apocrypha") were contained in the Septuagint,
which is the Scriptures used by Jesus, the Apostles and the early Church. Greek-speaking Jews used the Septuagint, but so many converted to Christianity that Greek-speaking Judaism ceased to exist not long after the time of the apostles. The canon of the Catholic Old Testament is a Jewish canon; it is the canon of Jews who accepted Christ.
Modern rabbinical Judaism is descended from the practices of the Pharisees,
who fixed the Hebrew canon after the development of Christianity and in response to Christianity. Protestants have chosen the Old Testament canon of Jews (Masoretic) who rejected Christ. Ironically, Protestant Bibles like the NIV had to refer to the Septuagint to correct certain portions of their translations from the Tanakh to match the Christological meaning!
The New Testament
actually affirms the authority of the Septuagint, which includes the Deuterocanonical books ("Apocrypha"). Here are a few examples...
Acts 15:17 ---> Amos 9:12 in the Septuagint. The Masoretic text contradicts the interpretation given by the Apostles.
Hebrews 1:6 ---> Deuteronomy 32:33 in the Septuagint. In the Masoretic text, this verse is missing.
Luke 4:18 ---> Isaiah 61:1 in the Septuagint. Jesus quotes the prophet Isaiah, which is missing in the Masoretic text.
Thus, either the Septuagint (containing the Deuterocanonical books) is authoritative, or the Apostles were in error. You can't have it both ways.