Because "overpaid" for what a teacher (generally) does and what a teacher (generally) is capable of doesn't approach what an intelligent and motivated person can earn in a real job as an engineer, surgeon, banker, small-business owner, etc.
In addition, many intelligent and motivated people don't want to spend four years of college on idiotized "education," and then spend their careers fighting through mobs of zombies in the attempt to do something worthwhile. Short work hours/work years, consequence-proof tenure, and so on are "rewards" for dull-witted drones, not for people with real ability and real education.
Those of the "best and brightest" who really want to teach some subject find themselves positions in private education and earn what they're worth in the free market, in the combination of monetary and intangible rewards that suits them as individuals.
+1
Any job performed well and honestly is a real job.