C. F. Keil and Franz Delitzsch on 1 Chronicles 27:16-17

1Ch 27:16-17 The princes of the twelve tribes. - The enumeration of the tribal princes, commencing with the words, “and over the tribes of Israel,” immediately follows the catalogue of the divisions of the army with their commanders, because the subjects are in so far connected as the chief management of the internal business of the people, divided as they were into tribes, was deposited in their hands. In the catalogue the tribes Gad and Asher are omitted for reasons unknown to us, just as in 1 Chron 4-7, in the genealogies of the tribes, Dan and Zebulun are. In reference to Levi, on the contrary, the Nagid of Aaron, i.e., the head of the priesthood, is named, viz., Zadok, the high priest of the family of Eleazar.