Rossi's age probably had a lot to do with his decision to move. He can't wait around, while they try to fix the turd.
And seriously, they haven't made much progress. Even Stoner was unsatisfied with the bike, when he left, then there was two years of "dream marriage" and no results. But it's somehow all gonna turn around next year? May be. But its been that same story for many years now, and they've fallen short of expectations.