Folks...keep in mind that the story in the Force Unleashed series was APPROVED by Lucasarts and from what I understand George Lucas himself. So...if you want to trash anyone for "canon" Mr. Blackman is really not your true target. Nothing happens with the SW franchise outside of fan created stories and such without the Lucasarts stamp of approval.
That said, I personally enjoyed playing TFU including the story and am looking forward to the sequel and beyond if there is a beyond. As for why Mr. Blackman left..perhaps he got a better job offer, perhaps he wanted a change of scenery, perhaps there was some kind of behind the scenes conflict...we'll likely never know unless he discloses his reasoning at a later date. Whatever the case, I wish him luck in any future endeavors.
"You'll find that many of the truths we cling to depend greatly on our own point of view."