Few Examples: Why Don’t Many US Airports Have 2 Major Airlines Operating Legacy Hubs?

In the United States, most large cities have a major airline hub, with some punching far above their weight. Across regions like the American Mountain West, all three major legacy carriers maintain at least one operational hub, with American flying out of Phoenix-Sky Harbor International Airport (PHX), United operating out of Denver International Airport (DEN), and Salt Lake City International Airport (SLC) serving as the linchpin of the airline’s regional network.