Possibly because becoming a software engineer often takes years of schooling, requires a level of aptitude that puts it out of reach for many people, and then r

Possibly because becoming a software engineer often takes years of schooling, requires a level of aptitude that puts it out of reach for many people, and then requires continuous additional effort to keep up with the field. If this sort of thing is not compensated for more highly than low skill jobs, much fewer people would do it. Of course this argument breaks down if being a tube driver takes as much intelligence, motivation, and education as a software engineer. I don't have experience in that field. But it does seem to me that if you hired a team of software engineers for a few years you could develop a system that would not require tube drivers to exist at all. Then the city wouldn't have to worry about grinding to a halt if anyone quits. But basically having higher wages for jobs that are harder to fill, or are more important to have highly qualified people in them, seems to be a system that works pretty well. Paying everyone the same wage seems to be a system that has largely failed anywhere it has been tried.