Basic supply and demand. The demand far outweighs the supply and the airlines simply don't care about service anymore. Even the first class fliers complain about lackluster service. Add the TSA Charlie Foxtrot to the experience.... There are no alternatives in the USA unless you have deep pockets; passenger rail travel is a freaking joke.
US Airlines don't have it easy either. They are at the mercy of the airport authorities for facilities and costs. Then they are at the mercy of the latest witless policy out of Washington that drives fuel prices. Don't forget about the wack-a-doodles they have to hire for gate and flight crew. Finally, they are publicly owned companies, so all the investor class and hedge funds care about is short-term financial performance.
Even the once great airlines like Southwest and JetBlue crumble under the US system.