And Brown would have been backup as well... so your comment is irrelevant.
If you aren't prepared to give a young guy 3 years to prove himself (typically what most borderline players are given) then why bring in an equally under-whelming young player rather than someone proven?
Just guessing here, but I figure that the established guys are out there weighing offers, while guys like Selvie, with potential, are subject to the waiver wire and don't get to pick and choose their spots. So you're going to hear about these sorts of signings first.
Obviously the staff felt that Brown just wasn't going to work in their scheme. So they released him. And they probably feel like Selvie might work, so they brought him in. It's not like they signed him to a multi-year contract, right?