One thing I haven't heard mentioned is that the huge capacitances of
power FETs are highly variable. They're essentially reverse-biased
junction capacitances, so they change dramatically over the period of
each cycle as the gate and drain voltages change. This tends to make
them lossy, and makes them difficult or impossible to absorb them into a
network. People have obviously found ways to live with the variable C,
but it's not a trivial problem.

Roy Lewallen, W7EL