LAX has the Pacific Ocean to constrict its traffic. Pretty much every other large city in the US has two airports at least besides Philly and Boston which are fairly close to New York. Next biggest city with only one is Detroit, which is also a very busy airport.

I used to work for Delta. Plane maintenance for other airlines and the government is a huge chunk. There’s entire teams in engineering who don’t do a single thing on Delta planes because they’re constantly doing repairs on external planes.

Also meteorology information or any other analytical information that can be sold to other companies, credit card program, charter flights.

I’m assuming in flight purchases and lounge status are covered under passenger revenue but potentially not.