The colleges don't pay very well and the degree required to get the job is very expensive and time consuming.
Even after you obtain your degree you will start out as an Adjunct Professor. These jobs pay about 2-4K per course.
After you have done that for about 10 years or so you might land a job as a professor at a community college.
Now you're making about $40-55K. Teach there for another 5-10 years until you finally get a job at a University to make that $80K.
Compare this (if you will) to the same person who leaves college with Ph.D and starts at $75K.
The difference in earnings over a lifetime is huge.
See: http://www.collegiatetimes.com/databases/salaries/salary?nam...
Also this person seems to have studied a fringe subject that would have a far weaker demand.