Maddison isn't picked for the same reason that Wes Hoolahan was often not picked for the RoI, i.e. not because of what he does, but what he doesn't do. He's in the squad for Southgate to work with to see if he can adapt better to the role required of him in this England team. England have made progress under Southgate for the same reason that we are now in the EPL, i.e. settling on an effective style of play and playing it effectively. When Maddison proves to Southgate that he can fit in to that, he'll be selected.