If you're selling a commodity it makes sense to sell a lot with very low margins. This means big organisations with a highly paid CEO and lowly paid minions.
A set of oak bookshelves is a commodity, and in the days of CNC that's true even for a made-to-measure set. There are still things that aren't though.
I don't quite know where flying instructors are on the scale of things, but mine (in a busy school) seemed to do quite well - certainly better than the average supermarket employee.