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).