Because he's the only RB (that I'm aware of) that's on the Browns' roster, and pickings are getting slim. Ben Tate isn't built to last, and I could see Cleveland doing something like trying to sign CJ (if the price is right). There's been a bunch of head scratching moves this offseason, and stranger things have happened.
If a decision seems like a really stupid and/or puzzling move, expect the Browns to make it.
They've also got Dion Lewis (out last season), Chris Ogbannaya (FB/RB), and Edwin Baker as far as the other backs worth keeping around for training camp/pre-season. Dion Lewis is the guy right now to take the back-up/two-back spot, since he was supposed to fill that role last season with Trent, with his speed to compliment the power game of Ben Tate. They have no reason to pay big money for another big back that won't be the #1 guy, especially one that probably doesn't want to be second fiddle to anybody.
I haven't seen any head-scratching moves that they've made in free-agency, as most of the dumb moves you guys have been hyping up in here never happened. That shows how much you guys know about what they'll do.