For the same reason that we encourage our playwrights to take classes in acting, directing, arts management, and even design. The more you know about the other disciplines you will be working with, the more respect and understanding you bring to the collaboration. Don’t worry, we’re not trying to turn actors into playwrights (although some of the best playwrights are also actors), but instead we are dedicated to making sure that an actor knows firsthand exactly how a playwright feels about the work they have created and the process a playwright goes through before sharing that script with a production team and then ultimately with an audience.
Yes, you will have to do some writing, but you won’t be evaluated on anything but being able to demonstrate your understanding of the craft of playwriting, not how good your play is. If a playwright can become a better playwright by finding out just how hard it is to memorize lines, sit backstage waiting to go on, find their light, say their lines, adjust their delivery, go for a costume fitting, find out there are a bunch of rewrites that have to be learned the day before they open, face a live audience, and all the other incredibly difficult parts of an actor’s job, then we’re pretty certain an actor who wants to work in new plays will be well served by learning how to write a play.