The extra complexity holds back frequencies in a couple of ways. The two that most immediately come to mind are: * More work and communication to be done per c

The extra complexity holds back frequencies in a couple of ways. The two that most immediately come to mind are: * More work and communication to be done per cycle means slower cycles. * More circuitry means more heat to dissipate. There are probably others, but I'm not a chip designer myself. I just sat next to a few.