The answer I think is quite frankly, because Trump is so new to politics, he really doesn't have the same type of network that most politicians have, so it takes longer to fill.

With the exception of a few generals, I think most Presidents were all congressmen of some sort. So they all had existing teams of people already in government. Those people knew people in government, and so on and so on. Everyone wants to move up on politics it seems, so it's probably easy if your contacts include people already in government, just reach out and say "Want a promotion?" Plus as we have seen with the swamp, people who are not rich love using politics to get rich, so it's easy to attract those type of people.

But with Trump, he mainly knows people who would be taking a huge pay cut to work with him, because they are already rich. Nobody except the truly patriotic are going to want to give up a lavish lifestyle to be slandered in the media, and have a literal target on your back every day. So he has to, at least temporarily, rely on some holdovers to keep things operating.

But I absolutely think he is thinking about, and actively working with people to replace all Obama holders everyday he is in office.