What really galls me these days is the fashion for literary types to write articles praising television. We don't need articles praising television. We need articles telling people to learn to play the fiddle, to reach ancient Greek, or reminding them to read something other than TV Guide. Nothing since canned spaghetti has degraded life more than television. Another mysterious question.
Teaching playwriting alone is a massive, dirty, grueling and most unrewarding job.
But more than that, playwriting of any kind is hard to teach because you can't teach playwriting in the abstract. You can only help a person to write a particular play, and your help can reach only so far because the play is unique and in that person, not in you. Moss Hart once said something that still strikes me as true. The problems that you can solve with one script won't help on the next one. And unlike screenwriting, the art of playwriting has little to do with storytelling techniques.