I mean, if we wanted our best and brightest (and most compassionate) to teach, we would pay them the best salary they could get with their degrees.
Note to good teachers out there (I'm a teacher too): I'm not saying there aren't any! I'm just saying that those doing the hiring can't afford to be terribly picky.
All the great song writers were mediocre singers. I'm talkin': John Prine, Steve Goodman, Townes Van Zandt, Leonard Cohen, Paul Simon, Neil Young, even Willie Nelson I would put in this category.
A weird exception is Joni Mitchell. IMHO one of the best singers of all time, and an a-list writer too.