I'm not that surprised, at least one of the beat writers discussed this possible roster crunch. He is the only optionable player. The alternative (for now) would have been losing Rodriguez on waivers, but he may still be the one to go next anyway, especially if they are committed to playing Kingery at 3B every day ('cause then you can't send down Haseley). Granted Rodriguez is nothing special but he is more versatile than Franco (and has the exact same numbers, except w/o the negative WAR). And supposedly loved in the clubhouse too. Most of the guys on this team have only played with Franco for one year (and very few for more than two), he may be well-liked but so is Rodriguez from what I gather.
I would also look at this as a good thing, given how streaky Franco is, and how he has sometimes responded to benchings. Maybe he comes back and helps in September, fights for a playoff spot on the longer bench. It's no different than when they sent Neris down.
I own a Franco shirsey and was really excited by his apparent comeback, but the guy has been mostly terrible when you include his defense. I know we get fond of our players, especially our minor leaguers, and then just assume the Phillies screwed them up, and I guess I prefer that to the "he stinks" reflex of many sports radio callers, but sometimes it actually is the players. And right now it's just the quirk of roster rules and no August trade deadline. (Honestly if there was an August trade deadline they'd probably still acquire a 3B.)