Its not that simple. Smaller transistors switch faster and consume less dynamic energy in the process. But the smaller the gate the worse the transistor is at being able to turn off the current and leakage current starts to become an issue. This is the main issue that is killing Moore's law as we are no longer able to ignore leakage current as it becomes more and more dominant to the entire power budget. This along with increased density of the circuits also cause risk of thermal runaway. These factors mean that as we shrink geometries the transistor architecture has to get more and more exotic (while still being manufacturable) to deal with these issues. So, yes the switching power is decreased but EVERYTHING else gets much more complicated.
