There is a lot of things wrong with US domestic airlines. But I think the #1 thing that is wrong is the quality of service. Onboard a US carrier, flight attendants are rude, not helpful, and impatient. I think they are still mad their pensions disappeared.
They bark commands rather than politely asking. They don’t attempt to help when people are struggling to put luggage in the overhead bins. They are irritable when you ask them for anything.
I remember flying back from Asia on United last year when sometime before landing I asked one of the flight attendants for the US customs and immigration forms. She responded with a very surly response to the effect that they had passed them out many times and was annoyed that I had asked. But she did say she would get them for me. She then proceeded to have a 15 minute personal conversion with the person seated directly behind me. I never received those forms from her.
I decided afterwards that I would never fly a US carrier to go to Asia. This past year I went to Asia several times and each time I had pleasant experiences on ANA, Asiana, Singapore, and Korean Air. There is a world of a difference. You can yell at the flight attendants on these Asian carriers and you will get a gentle apology. You can be a body builder and they will still attempt to help with you with your luggage.
Not only in terms of quality of service but they are world class in a different aspect. They can fit in the aisles with plenty of room, are easy on the eyes, and they didn’t roam the earth with dinosaurs. Damn those US discrimination laws and labor unions.