It depends upon the individual. Some teachers are the most highly-sought consultants in their fields (and often even wider fields, and greater areas), while others sleepwalk through from paycheck to paycheck, couldn't give shit less, and are practically worthless.
Teaching, itself, is a most noble pursuit. Some individuals may place a higher value on fulfilling the gift of teaching, than to chase every thin dime that presents itself along the way. When you are merely a dime-chaser, you have become a caricature of yourself, and may be considered even more worthless than a bad teacher.
Like everything else in life, it comes down to the individual.