First, old fashioned mainstream Republicans (type Dole) still make up the largest GOP voter group. They don't make as much noise as the tea party types -- too busy buying Metamucil -- but they vote.
Second, as Nate Cohn has noted, although blue states elect few Republicans to the House, they still elect a large share of convention delegates. and these delegates tend to favor traditional candidates. For instance, Connecticut, Massachusetts, and Rhode Island have zero representation in the House GOP conference, but they all send delegations to the convention.
Third, Henry Olsen adds important detail about the nomination process:
Many movement conservatives have circled March 1, 2016 on their calendar. That’s the day that seven conservative, Southern states have banded together to hold “the SEC Primary”. The thought is that if the most conservative states vote early, that will give a movement conservative candidate the momentum needed to take on and defeat a more moderate opponent. Sen. Ted Cruz in particular has staked his hopes on that notion, telling audiences that March 1-voting Southern states are his “firewall”.
This strategy is more likely to result in a political Pickett’s Charge, a courageous gesture that will become known more for its futility than its wisdom.
That’s because RNC rules require states that vote between March 1 and March 15 to apportion their delegates proportionally rather than by a winner-take-all method. I discussed the potential ramifications of this last September, and sadly it looks like my worst fears have come true.Fourth, the party establishment does not have final say, but it still counts. In this case, it is not just that the party establishment is cool toward the outsiders and hardliners, but it will do whatever it takes to stop them. (I do not count Fiorina in this category. She does not hold office, but she is no outsider.) In particular, GOP senators hate Ted Cruz. He crossed a line when he called Mitch McConnell a liar on the House floor, so now McConnellwill do everything in his power to take him down.