Adding the locomotive at Sacramento would cause considerable delay. You would have to:

1) Cut off locomotives from the train (place train in emergency, cut out HEP lines, etc.)
2) Move over and pick up the electric locomotive
3) Cut in the air brake system, HEP, etc. Perform air test of consist.
4) Return to the train, restore HEP and brake lines, perform air test of train.

Much easier to do this in Oakland and make sure everything is working properly. Number 6 will receive a delay in Denver when the dead locomotive is removed from the train.