Mechanics Exam Question (USA)

[youngump]

In the Two Umpire System with R1 at 1B and a ground ball to the infield the plate umpire should?

There are two similar answers for this question. After trailing the BR, one involves stopping to watch the play at 1st and then moving for the potential play at third. The other involves moving as the lead runner approaches 2B.

Reading the mechanics it's clearly the latter that is intended and like so many other things I've been doing this wrong. But now I'm left wondering what in the world sense this mechanic makes. If I'm not going to be around to help with the play at 1st (and there's no way I will be if I have to move away from my position before the runner from 1st gets to second) why am I even trailing, why not go straight to the pitcher's plate?