• They did not tell him because they did not trust him.
• They gave a man who does not like to read a brief to read.
• They told him, but he was not listening
• They told him and he was listening but he just did not care
• He believed what Putin was telling him over his own intelligence community.
• He made a decision and sent that decision back to the intelligence community and military to implement.

I would like to believe that the last option is what happened, but unfortunately that there is nothing in the past that makes me think this is true. Which leads the remaining five possibilities, none which are good.