I don't think public figures come out for attention, as the media makes it out, but so that some LGBT kid in the Bible Belt who may be contemplating ending his or her life has hope! They too can be an actor or actress! They too can be an Olympian! They too can be anything they want to be.
Luke Evans has the talent, not to mention the biceps. Having appeared in Clash of the Titans and the recent Three Musketeers, and with a part in the upcoming Hobbit movies, his Hollywood resume is filling out nicely. So why now hide his sexuality?