I doubt most teachers have ever expected to make a lot of money teaching. Most choose to teach for the reward of influencing youth and making a difference in the world. Some are, obviously, just plain ol dirty pedophiles. So, maybe these few are in teaching, and have been, for all the right reasons and want nothing more than to continue.
Some start off teaching, get their Masters, figure out that teaching is for the birds, and then go onto Administration--that is where the money is. Who wants to be around a bunch of brats who expect you to Give them grades, their parents expect you to GIVE them grades, and the Admin and Principals don't have your back? Who'd want to sit around and teach to a test so that the school looks good when it comes to standardized tests? Some then go onto being professors (bypassing the grade school route), where there is more money.
Due to less quality of people becoming teachers today, you have a glut of people who need not be in the classrooms, but need to be painting houses, mechanics, doing nails, porn, or cheerleading