Its just another continuation of our class system writ large. Senior Officers only always get the OBEs in the RN, CBEs for lesser officers and Senior Ratings, BEMs for the remaining. Its just the same old **** pecking order.
Whilst agreeing with your general point, you are a bit adrift in your grasp of the honours system. The CBE is a higher award than the OBE, and would generally be awarded to Commodores/Captains RN and equivalent. OBEs would tend to go to Commanders and Lieutenant commanders and equivalent while MBEs, which you omit from your list, possibly confusing them with the BEM, go to junior officers, WOs and ORs. The BEM, which used to be awarded to OR's is now awarded quite sparingly, mainly to civilians for charity work.