Why don’t people settle in the Western Area?

This is a question that’s lived in America for a long time. Well, it’s mostly because there are a lot of major cities like NYC, Cincinnati, Chicago, and much more. But the real reason is because due to the Rocky Mountains in the Central USA, clouds cannot pass through because of how high they are, making the area very dry. That’s why there are lots of wildfires in that area. If you look at America from space, you would see that east of the Rocky Mountains, there is a lot of 

light there, but the other side doesn’t have much light, only cities like Seattle, LA, and Las Vegas only have light. But why? Since states don’t have many major cities, people there don’t need light. Well, that’s all. Thanks!