Or, you know, before POTUS decided that we don't need a State Department.
Trump simply doesn't trust other people to speak for him or act on his behalf. He has his own very unique view of the world, a world that looks as if it is being heavily influenced by the numerous skeletons he has in his closet and those that know where those skeletons are and what tale each of those skeletons will tell. Even his handpicked SecState Tillerson is outside the very exclusive world that Trump has progressively retreated into.
From the very get-go of his term in office, Trump displayed his penchant for trusting his own family members first and foremost to run the ship of state despite the fact that his children had absolutely no experience in running even the most mundane daily chores that seasoned bureaucrats knew by heart. Trump also hand picked whatever cabinet members he could draw on from his own campaign staff and those who closely backed him where loyalty was obviously the most important qualification and being from the big business big money donor class the very next on the list.
Trump is also very suspicious, wary and very afraid of those gov't agencies that he cannot have personal control over. IMO, a lot of that fear is due to his not having anything like the connections and deep penetration into the workings and echelons of gov't that politicians with long gov't service would have established for themselves prior to running for office.
Trump has very much to hide from the nation he leads and the only way he can protect these closely held secrets of his is to have the least amount of people involved in the decision making processes of the policies his agenda dictates, especially where he has made personal commitments to others that involve his business dealings and how he is using his position as POTUS to maximize his potential for ROI.