Why was it determined by the Rabbis that the 24 books of the Bible only include those books and not more?Why weren’t other holy books, written later in time, included in the Bible ?
The Bible (Tanach) isn’t a collection of holy books. It is the collection of prophecies that were given to Israel for all generations. There were other, more local prophecies (such as when Saul went to ask the prophet where his father’s donkeys were). But the ones that were for the whole nation became the Tanach.
When the period of the Second Temple began, the world was on a very different spiritual level and prophecy had ended. There were many holy books written afterwards (the Mishnah, the Talmud, the Shulchan Aruch…), but they are in a different category.
Best wishes,
Michoel Reach