Because it's a big hoax.
In fact, the union-thug babysitters get paid plenty, way more than they're worth, (not to mention their pensions) especially considering their pathetic "learning results". Kids now are dumber than ever, and especially when measured against foreign students. That being true in spite of the fact that we have among the highest per-student costs in the world.
...given the technological improvements of the last 50 years, why isn't the U.S. far wealthier than it is? How could it be that average wages have not increased in 40 years?
Maybe it has something to do with the astronomical, ever auto-increasing budget, which consumes all tax revenue, and then borrowing the balance from the likes of China. Most of the Trillion$ of approps goes to pay the salaries and benefits of the endless hoards of bureaucRAT hacks, and of course, the aforementioned educRATs.
Maybe if we had a fraction of the greedy government parasites, the American public could send their kids to private institutions and pay real educational instructors what they are really worth. (and fire any drones)
Teacher pay varies a LOT depending on where the teacher is located. Here in southeast Tennessee, starting pay for a teacher is in the low 30s. In NY City, it's 2 or more times that. Granted, the local cost of living is better here than it is in NY City, California, or other inflated markets.
That's not to say that the teachers always do a good job, or that the students are gaining useful knowledge. I think that there's a great variance as to what is taught/learned and what the rate of pay is for that.