Really the codeshare was most beneficial to CO of old. They had no flights to Heathrow at the time from EWR, so codesharing on VS gave them "flights". It also gave them flights from various big US cities where they had no presence to LHR. Now, however, UA/CO serves most of those cities from LHR (SFO, LAX etc) and can feed efficiently to others.

I suspect it will eventually go away.