You can't just turn up clockspeed and expect linear increase in performance. The chips are packed so dense with transistors that the chips have to do some magic to be able to operate at those clock speeds without frying. Desktop parts don't really care about energy efficiency and are thus designed to be able to operate like that since max performance is more important than efficiency. Microarchitectural design decision allow engineers to pick tradeoffs for where they want to place their chips in the market, but most major advantages between chips come from fabrication. And these days there aren't much gains left to be made there.