The other two divisions have a fixed sequence. This one does not. Rabbinic tradition records one order for the books, the great Tiberian codices arrange them differently, and printed Hebrew Bibles follow another arrangement again, with the position of Chronicles, Psalms, Ruth and Daniel varying between them. Nothing doctrinal turns on it, but the variation is a symptom: a division whose internal order was never fixed is a division that was assembled late. The contents are correspondingly mixed.
Psalms, Proverbs and Job are poetry and wisdom; the five short scrolls are read at festivals; Daniel is apocalyptic; Ezra, Nehemiah and Chronicles are historical narrative that overlaps material already told in the Former Prophets. There is no single principle grouping them beyond not belonging to the first two divisions. That is probably the right way to understand the category.
The Torah closed first and the Prophets second, and this division is where the remaining authoritative books ended up, which explains both of its oddities at once: why its boundary was still being discussed in rabbinic sources when the other two divisions had long been settled, and why its books needed no shared genre, period or purpose in order to belong to it. It is defined by exclusion from the earlier divisions rather than by anything positive its members have in common.