You could say employers are greedy and hoard excess profits while keeping wages low, or you could say that they generously provide much needed jobs to a struggling low-skill labor market. Both are true. It would be nice if low-skilled labor drew higher wages, but wages above the economic rate are just another form of charity. You don't compromise your value of hard work by choosing to pay low wages, you just lack charity.
In regards to your comment that "You don't compromise your value of hard work by choosing to pay low wages, you just lack charity." Perhaps to a business owner in a competitive market, paying more than prevailing rate would feel that way. But on a broad societal level, it's not charity to hold that everyone who works full-time should at least earn a lower middle class subsistence. If this were polled, broad majorities of progressives, conservatives, and libertarians would agree that work should be enough to raise one out of poverty. Nonetheless, we lack the political will to enact any kind of reform to realize that, because we worship "wealth creators" and the "invisible hand," and, for instance, raising the minimum wage is hence off the table.
If we really truly valued work in more than a symbolic manner, this wouldn't be the case; the libertarian right would be providing concrete policy proposals that would actually address the problem in a way they consider non-coercive. Instead, we hear post-facto justifications for our inequality, or even arguments that it's a good thing. Hence, I stand by the idea that we don't "value," as in moral value, work, no matter what we claim our values are.
Teachers are primarily public servants in the US (before college, and probably even the majority of college professors though I won't make a wager on that). Their pay is directly determined by our culture as reflected by who we elect and how we vote on referendums. Clearly, our culture does not value teachers if me choose to pay them poorly with respect to their scope of responsibilities and the time required to perform their jobs. Along with 6-8 hours of instruction and student interaction each day, their primary time for prep and grading is outside of those school hours. Pair that with having to sponsor clubs or coach athletics to earn a little more money to make ends meet (especially if they're the primary or sole earner or have children) they have to commit to 12-16 hour workdays throughout the school year. And then we require them to maintain certifications and professional education (not bad things on their own) that require spending losing many evenings and weekends to satisfy (and sometimes money spent from their own pocket just to be allowed to stay in their job).
They say teachers are highly competent, qualified people who work hard and deserve more pay.
If it is true that teachers are generally good, then they are paid appropriately to attract highly competent, qualified, hard working people to do the job.
Ironically, it is because teachers are so highly valued by our culture that they are not highly economically compensated.
Apparently, there are non-economic incentives to work as a teacher.
If you think a lot of teachers are complete clowns, then teachers are probably not compensated appropriately.
So, if teachers aren't paid enough then a lot of teachers should be fired and replaced with superior candidates.