Cumbres Turnmtable

Question for the folks with knowledge:
Why did the Rio Grande come along after the Cumbres Pass line was done and add a turntable to the west (Chama) leg of the wye? I am trying to work out the logic of that one. The only purpose that I can really see is in plowing the wye you could turn the engine and plow the east leg of the wye which otherwise is rather hard to get to with a plow. (Assuming the ENGINE has a pilot or wedge plow attached. I can see no way to plow with a separate plow. (Neat switching puzzle, turn the plow and engine with the east leg of the wye blocked.)
Any thoughts?
Frank