Whether you agree with the decision or not, it should come as no surprise. Trump is an isolationist through and through. He distrusts the entire foreign intelligence apparatus, which has been wrong about every foreign intervention since the Kuwait War, and thinks only in terms of American interests. Personally, I find this point of view refreshing in a US president. I wish GWB had this kind of hesitancy before he got us entangled in Iraq.
The truth is, all countries exist as the result of the use of force. If countries are going to exist thanks to us using our force, then we ought to be getting some benefit.