Rulesman is correct. Some crews have ineligible officials. Ineligibility can be based on amount of service, ratings, or how long ago it has been since an official worked . Nobody is going to work two in a row.
Moreover, the philosophy is to take the top officials from each position. You can strive to be the best umpire but if the SJ on your crew is ineligible based on experience, why punish the umpire?