Well yeah, but in places like SF and NYC, supply is limited by available space. We could house people in 6x6 cubes in giant rectangular buildings to be really efficient, but nobody wants that. So what do you do when your supply is limited, and the poor and middle class are being pushed out of your city?
Cupertino already is fairly high-density, at least downtown. And I don't think anyone suggested bulldozing anything, just allowing people to build what they want, which they currently have a very hard time doing.