Okay I don't know where to start.
1. Januzaj, Varela, Borthwick Jackson are not let go as they are out on loan to get more playing time so they can be seasoned for Mourinho in the future
2. He doesn't really need those players since he has an expense of players to work with that he has notched from teams with the teams not realizing how good they really are. (Think Pogba, Bailly, Mkhitaryan)