There would be no reason to inform Trump because he wouldn't understand he almost created World War III

 There is no way someone as incompetent as Trump would have understood what Milley was trying to do to prevent world war three caused by Trump's basic incompetence. Trump NEVER was qualified to be president and always was incapable of preventing World War III while he was president.

Trump lives in a completely unreal world that has to do with his personal finances and nothing else really. He is like a reality show star who someone put in as president but who was always completely unqualified to actually be president. He reminds me a little of the president of the Galaxy in "Hitch hikers Guide to the Galaxy" where the guy is off his nut and just flamboyant and is almost killed by those who protect him many times because of his complete incompetence.

If Trump was actually about keeping the U.S. safe from the world or UFOS January 6th would have never happened at all.