Power Dissipation in Switching Regulator

There are many things that cause power loss.
When current passes through a diode, one form of loss is the Voltage Forward of the diode X Current in the diode. (0.65V X 2A)
When current passes through a MOSFET, one type of loss is "Resistance Drain-Source on" & the current D-S causes loss.
There is power loss because of resistance in the Printed Circuit Board.
Then there is "switching" losses. As the MOSFET turns on/off there is a very short period of time where there is "AC" loss.
The IC needs power to work. That power is lost.