This is somewhat of a digression, but the extremely low rate of teacher pay (for a job that requires a Master's degree) limits the pool of available teachers greatly. The people taking these jobs typically must have some other way of supporting their family; either their spouse has a higher-paying professional job or they are the beneficiary of some other form of generational wealth.
But we tend to lose the teachers who must make ends meet their own selves on a teacher's pay. There is no good economic argument made to become an elementary school teacher.