I agree that the nomination process is absolutely important to how the system functions, and plays a really big role in whether we get extremist or moderate candidates in the first place.

The interesting part is that the presidential nomination process is essentially constructed by the parties themselves. It’s not in the Constitution.

However, your point about NY, LA, and Chicago is wrong. Those three metro areas combined have 13% of the population. If you win 100% of the vote in those three areas, you still would have to get 42% of the vote everywhere else in order to get to a majority.

Campaigning in the same area has diminishing returns. This is true whether we talk about visits or advertising. The first million dollars a candidate spends on a House race have a much bigger effect than a second million dollars. With a national popular vote, you’d be foolish to concentrate all of your efforts in one area.