Trump lacks the self-control to become “so presidential you people will be so bored.” He is incapable of doing it. As in “cannot.” No amount of coaching, prompting, begging, teleprompters, speech writers, or threats can make him do it, because he cannot.
That is the nature of an untreated mental illness such as his.
With treatment, he could perhaps learn to recognize the problem and learn to overcome it, at least somewhat. But people who think he's being calculating, or alternatively, those who can't figure out why he does stupid things, are ignoring the fact that he's mentally ill.