1) He has absolutely no imagination, and is entirely incapable of deploying a formation that is different from the one he is used to winning in. Mainly, 4-3-1-2.
2) He is entirely incapable of making game-winning or momentum-changing substitutions, because his go-to plan when things aren't working out is: "hey guys see what we've been doing for the past 65 minutes? Let's do more of that, but better somehow! That'll show'em!"