Why? It is extremely difficult to use miles to upgrade CO flights. It is almost impossible, especially on the LAX/SFO/SEA-EWR flights.

My question is:
What is my chance for getting an upgrade on the morning EWR-LAX nonstop flight on a Wednesday and on the noon LAX-EWR flight on a Wednesday as well. I want to confirm in advance, but it is apparently impossible.

Thanks,
Carfield