The way it was explained to me...I could be wrong but it makes sense. United is maxed out on the number of 70 seaters flying for them so they can not add anymore on the code ( their scope at least has some limits). So if management wants to fly them out of IAH, CLE, or EWR, they either need to put it on the CAL code or reduce a flight on the UAL side. Make sense??
Please correct me if I'm wrong I don't know much about United's Scope.