If your degree/passion is for something like literature, history or music then teaching high school is, relatively speaking, one of the better jobs you can get where you can focus on your subject and use your degree. If someones degree/passion is in math, physics or programming then they simply have so many more options that the chances they end up in teaching is much lower.
You can be, just not in school - only at university level and above, when some time ago someone figured out a trick to combine research work with teaching responsibilities. This works well as long as there is no significant market demand for a given discipline.