"Stick around" is the key phrase - he was already here. Lerners don't like paying a guy not to play. I think Rizzo would have dumped him if he hadn't been prohibited to do so. Montero isn't here, he's a known troublemaker, and I don't think Rizzo thought this through very carefully.
If you're a marginal player, having an attitude doesn't help. Teams will tolerate more crap from a guy who produces. That's why they eventually ran Papelbon out of town and out of baseball. Guys like Nook Logan, Lastings Milledge, etc., were the same.