Smaller transistors can flip state more quickly with less energy, so usually a die-shrink allows higher frequencies. There's a limit to how much you can crank

Smaller transistors can flip state more quickly with less energy, so usually a die-shrink allows higher frequencies. There's a limit to how much you can crank these things before power consumption becomes ridiculous and heat dissipation is impossible. You can make a 10GHz CPU if you're prepared to require a massive liquid helium cooling system and have a power consumption of 15KW.