Dunno, maybe it doesn't go back to the panel, or code satisfying ground source. It is easier with two wires. The picture shows 3 in/outs with a plug though. I wonder how that goes. I would be cussing i'm sure.
I see what your saying though. The difference between getting a job and not could be that redundant ground one could pull in. Or sizing the conduit one size smaller if not for that redundant ground
