Power use increases quadratically with voltage. You want small transistors to keep the voltage and power use from getting out of hand. You also need to increase voltage if you want to increase clock speed.
Electric signal travels in a conductor roughly 15 cm/nsec. With 3 GHz clock speed the electric signal travels travels roughly 50 mm in one clock cycle. Largest microchips are 30 mm across. You can't double the dimensions without dealing with the signal lag. Delivering the clock signal to every part of the chip in sync is already a problem. Modern microchips use lots of extra circuitry just to deliver the clock signal properly.
Power use increases quadratically with voltage. You want small transistors to keep the voltage and power use from getting out of hand. You also need to increase voltage if you want to increase clock speed.
Electric signal travels in a conductor roughly 15 cm/nsec. With 3 GHz clock speed the electric signal travels travels roughly 50 mm in one clock cycle. Largest microchips are 30 mm across. You can't double the dimensions without dealing with the signal lag. Delivering the clock signal to every part of the chip in sync is already a problem. Modern microchips use lots of extra circuitry just to deliver the clock signal properly.