Except a lot of the time, the job market is a lot more complicated than that and years of study don't always correlate well with eventual earnings. I have a pretty basic bachelor's degree in computer science and I have never once struggled to find reasonably high-paying work wherever I am. I have a friend with two bachelors' and a master's who has studied far more and far harder than me, and she has struggled to find work anywhere in the country, and when she has, it's been far lower paid. My brother has studied at least as long and as hard as I have, and is as much an expert in his field as I am in mine, but because he got a vocational qualification in a less well-respected profession, he works twice as many hours as I do for half as much pay.

So while I broadly agree that there will always be some necessary income disparity, I think it's disingenuous to use such simple examples and present this as a "work hard; get paid more" situation. In practice, income equality has more to do with whether the skills you have are socially valued or not.