Romney doesn’t have the delegates to win a first ballot nomination
His current national polling average is about 32% right now. If he wins all the winner take all states and gets only roughly 30% of the rest, he’s about 130 short. There aren’t enough super delegates to close that gO even if they all broke his way.
It is no longer good enough for Mitt to win. He has to win with majorities or else it’s a brokered convention.