If you think if it yourself, does it fair for UA still grant you DEQM when they don't earn all the money from you ?

DEQM is to attract people purchasing ticket from that specific airline and flying for that airline only. As even you are on UA metal, but you bought your ticket from CO, which means some of the money get into CO's pocket (true ratio of codeshare flights I have no idea). It is always the catch either you buy a more expensive ticket on UA and fly UA, or buy the cheaper ticket and forget DEQM, there is no double dipping.