Sony didn't trust Raimi after 3 movies that made nearly a billion dollars each (over a billion, if you include DVD and merch sales). Why would they trust Cameron more, just because his movies have made slightly more? In Sony's eyes, big name directors like Raimi and Cameron are more of a nuisance than an asset, because they are more difficult to control. Studios worry about control more than they worry about box office potential, because in the studio's mind, the more control they have, the better they can ensure a product's success. James Cameron is not someone that studios control, and Sony just let their current director walk because he would not let them control him. Like I said, Cameron is probably the last director they'd consider right about now, save for the likes of Uwe Boll (in fact, that's probably the only list you'll ever find James Cameron and Uwe Boll close to each other on).
