Let's change the terminology a bit here. A professor is someone with tenure is on a tenure track. A lecturer is someone who is not. The article isn't talking about professors, which in the USA relies on research, publishing, obtaining grants, and tenure. Yes, a lecturer teaching a low demand subject is going to have a hard time. Just like most positions, there exists a hierarchy. The reason why this doesn't exist for primary and secondary educators is because of unions and that can be argued either way.