United States have 172 Large airports clustered around the coasts and metropolitan cities, 686 medium airports spread among major cities, and 13,890 small airports scattered across the country. If you look at the point distribution of airports across United States, Nevada, Montana, Wyoming, and Utah has relatively lower distribution when compared to the rest of the country. Is it because of the geography or the trade-economic status of these states? Here is the visualization with embedded links to the Wikipedia pages of the airports –

United States Airports