Why would anyone want to be a poet? If that question seems too broad (or too harsh), let’s try a more modest one: Why would someone who’s already mastered an art form that is vastly more influential and lucrative than poetry — fiction or songwriting, for example — want to be a poet? The most famous poets aren’t famous, the richest poets aren’t rich, and not even the best-loved poets will ever enjoy the devotion inspired by Barbara Kingsolver, let alone Lady Gaga. So when a superstar from another arena turns his or her attention to poetry, the result can be like watching the Super Bowl M.V.P. forgo an entire season to devote himself to foosball. “Why,” one wonders, “is this person bothering?”