There are few big careers to be made out of poetry. Although sometimes, as in this case, prize money is involved, it is hardly enough to risk your reputation for. Most of what we get from writing poetry is the release of creative tension and the respect our peers. What is to be gained by taking someone else's poem and calling it your own, especially when you're bound to be exposed at it?
Despite the plagiarist's confession and apology, I still don't have answers to these questions. Here is my Ottawa Citizen article on the subject: