(Don tin foil hat.) Perhaps he told Obama that he would not allow his troops to be used in Obama's allies' plans to make the inauguration into a circus. The timing of this may be because the plan is to change commanders at a critical time, causing chaos and then blaming it on Trump. After all, the general was relieved when Trump was sworn in, right? And, he is black, so a racist Trump relieved a black general as soon as he was sworn in. Never mind the facts, the press will send out that story.
If that werew so...Trump could promptly re-apppoint him at 12.02.