Because. in my opinion, Perez is a better pitcher than Romano at this point. Keep the better pitcher. They can find ineffective innings anywhere. No need to prioritize keeping some one for that.
Nobody is going to claim Romano. He can go to AAA and start and work on his pitches. He'll never be effective until he learns a change up. Not as a starter or reliever. He needs innings to do that. In the bullpen, he never even throws it.