No One's Queuing up for Joyce's "Exiles"

Why don't great novelists makes great playwrights, and vice versa? This article from the Guardian Unlimited delves into that issue. In passing, Stoppard's "Lord Malquist and Mr Moon" is described as "far too slick and ingenious to carry any weight: that boulevardier's juggling, so delightful and paradoxical in the plays, just looks cheap on paper."