Why do leftists think that the more educated a person is, the more that person should make?

A common refrain I see from the left is that government hacks should make more because they are more "educated". I'll accept that at face value, which begs the question, what in the hell does that have to do with it? Education without marketable skills is worth squat. Zero. Why on earth should a hippie who spends 10 years in college and ends up with a PhD in "Human Studies" make a boatload simply because he spent 10 years avoiding reality? I wipe my butt with worthless degrees that provide a person with no marketable skills.