Because discussing, ananlyzing, and grading essays takes time, effort, and subject knowledge on the part of the teacher, whereas role playing comes in a canned program and eats up large quantities of class time which might otherwise have required even more time, effort, and subject knowledge on the part of the teacher.
Ah, excellent point!
I distinctly recall producing an essay on "The Diary of Anne Frank" without having read the book. Now *that* was creative!
bttt