If memory serves me correctly, prior to that he had Tom appointed as the head of the family while Michael was away; there was that scene where Michael manipulated Tom by calling him his brother, which he definitely knew Tom always wanted to hear.

Perhaps Rocco or Neri complained to Michael about Tom, or on the other end of the spectrum, perhaps Michael saw Rocco and Neri listen more and more to Tom and he wanted to put him in his place.

Or maybe, as you say TB, because he could. But I always found that scene and their dynamic very interesting as well.