They'd rather give their young arms like Burr, Frare, Hamilton, Covey, Ruis, Stephens, Vieira, etc a chance versus holding a guy on their 25 man all season. Its not really that hard to figure out. They have plenty of bullpen options, didn't need to add a fringe guy into that mix that HAS to stay on the 40 man all season.
I would have been fine with them rolling the dice on Ferrell if he fell to them or ever Tyler Jay, but I am not at all disappointed.