I agree with your experience, it does feel a bit insane, but just to point out this is the result of too much competition selling a commodity product rather than a monopoly.
You need to break up the cartel model so that (e.g.) Delta has real competition for routes to Atlanta. If I look at nonstop flights from LAX to Atlanta for a random day (Apr 1, 2024) your options are: 1 American flight, 1 Alaska flight, 3 Spirit flights (way more expensive) or a Delta flight just about any time you want to travel. That's not "too much competition selling a commodity product" - it's what I would expect from cartel pricing. There is a thin veneer of competition, but Delta owns that route - 90%+ of traffic is going to fly Delta.
I will say I was amazed by how few options I had to get from JFK to Denver and the price was insane relative to a transatlantic flight, so perhaps the market is structured differently.