2-Man Umpire System - B-position

[BSBAL18]

Question regarding the B position for a 2-man system.

Just trying to understand clarity from more senior officials. While the book states to be in the "B" position (runner on first only, otherwise you're in the "C" position). WHY can I not just always be in the A position for no runners on base, and then C position for all other criteria?

With a runner on first, an attempt to steal second with umpire in C position is a much better angle (right?). And i would assume the B position is to be closer to first base for pick off attempt, but i have found being in the C position is only ~10 feet further with the same angle, and i do not see any benefit. Is there another reason for the B position besides pickoff attempt?

Just trying to get some feedback on why C position isn't preferred, especially on an attempted steal of 2nd base. Thanks!