Christopher: When I was in college, many - not all - teachers college students told me they made this choice because, unlike arts and sciences students, they didn't have to take a foreign language or as many science courses. My high school was run by the local teachers college (college seniors getting their first round of practice on us), and while I recall a couple teachers who were quite good, most were just going through the motions of getting their college degrees.
I am often reminded - in my own work - of the saying: those who can't do, teach; those who can't teach become school administrators. Over the years, I have encountered a good number of intelligent, well-motivated, sincere teachers, many of whom give up teaching out of the frustration associated with having to satisfy all of the bureaucracy demands that have nothing whatever to do with learning. I keep coming back to Mark Twain's admonition to never let schooling interfere with your education.