Because he has not proved he can, it's that simple. You say Jones has all the attributes, but he does not possess O'Shea's most commendable and valuable attributes, which are his reliability, consistency, versatility and dependability.
Jones is inexperienced and unproven, to suggest he can just adapt to playing an unfamiliar position simply because he is a better technical player than O'Shea, is nothing more than wildly optimistic speculation on your part, and how you can believe that is a reasonable basis for a credible argument, i find a little bizarre.