According to Dan Bernstein, his Cubs source tells him that team management really wants Silva to make the rotation. Another part of the equation is that they are worried they will burn out the back end of their bullpen (Marmol, Marshall, and Wood), so they would like to have Cashner in the bullpen to lessen their workload. I have no idea how reliable this "source" is, but I judge it as credible simply because it would be the typical Cub thing to do... valuing a 6th/7th inning bullpen guy over the development of a potential top of the rotation starting pitcher.