I find the quality of airlines symptomatic of economic growth and development within a reason. The US domestic airlines are declining from age, wear, and tear, and a tendency not to invest in America anymore. In other words, domestic US airlines are just focused on profit optimization and not enough on how they can upgrade their aging fleet. In contrast, international airlines have dramatically invested in new airfleets realizing the value of their assets
Ah, the financial aspects go far beyond what most of the public realizes. The US government
doesn't intervene when it should, and
intervenes when it shouldn't. There are investments that each airline is supposed to make, few do it, and the government mostly just says, "You are naughty. Now you had better start following your legal requirements." To which the airlines pretty much reply, "Uh, yah, we'll get right on that... <hahahah>" Then they whine, "we don't have any money!" and the government bails them out.
Southwest Airlines, which is so often ridiculed, has been operating in the black, every year, since it started operations. Other airlines, with a greater revenue base and approximately equal operating costs, generally do not. What's the difference there?
Delta has been one of the (consistently) worst airlines I've dealt with, including flights, ontime departures & arrivals, customer service, and baggage. They even tell you an outright lie, if you ask direct questions about cancelled flights and they don't want to tell you why.