When Barack Obama began his second term, he made some new cabinet appointments. Hillary Clinton had let it be known well ahead of Obama’s reelection that she was not interested in serving a second term of Secretary of State.
That’s not quitting. It’s a natural and orderly completion of a term of appointment without committing to reappointment.
It’s customary for appointments to terminate with the completion of the term of the officer who made the appointment—in little clubs as well as in big countries. A presiding officer who is returned to his or her position for another term may renew appointments, provided that the appointees are willing to continue in service, or replace appointees.