Obama had a different agenda and a different way of running things.
This style of turnover is more common in a building project or a company where you bring in people to fulfill a purpose and then replace them with someone else once that objective has been met. For a person like Donald Trump this is how he always did things. Bring a person in to fulfill a purpose once objective is met person leaves and you bring in someone to handle the next thing. If person A takes to long and objective is delayed replace them with someone else who will do it.
Understanding the man helps to better understand why he was picked for the role he is in.
A good example is Mosses he spent 40 years as a prince of Egypt learning how to be a leader. Then he went into exile for 40 years in the Sinai learning about the locals where all the watering holes where as a shepherd and essentially how to live as a nomad in the very area he would be leading the Israelite through in exodus.
He was 80 years old when he came back to Egypt to gather God's people back to the holy land. He spent the first half of his life learning to be a leader and the 2nd half learning about how to live in the wilderness of the Sinai he then spent another 40 years leading the Israelis through that wilderness. the first 80 years of his life helped shape him to be the man God wanted to lead his people to the promised land.