Maybe he knows something you don't. Maybe the Chinese or North Koreans meddled also.
And by the way you are repeating left wing exaggerations, first they agreed Russians meddled, that's a little different than "hacked". Buying Facebook ads and creating Twitter accounts don't really qualify under normal definitions of "hacked".
And four agencies were involved in the January assessment about Russia: CIA, FBI, NSA and the Office of the Director of National Intelligence, to get to 17 you have to individually count all departments overseen by the last, like the Treasury and Energy Departments, those departments did not individually sign on to the report.