Matthew Poole and continuators on Hebrews 7:23

23 And they truly were many priests , because they were not suffered to continue, by reason of death .

This further demonstrates the excellency of Christs Priesthood above the Aaronical for its Singularity and Self-sufficiency; whereas theirs was for the Multiplicity of it, weak, vanishing, and mortal, like themselves: They had multitude of Priests together under the High Priest, to manage the Service, and above seventy High Priests beside their Sagans, such as were to officiate for them, if at any time they were legally disabled from the Institution of the Aaronical Order, to the Destruction of the Temple, and were made according to the Law successively.

Death cut them off one after another, they were all mortal, and could not abide neither in their Priesthood or Life, Exod. 28.43. Death transmitted that Priesthood from one unto another; 'tis the Priesthood it self by the Succession of a better, was abolished, and did expire, so frail, passing, and imperfect was both their Persons and Office.