Why?
First off, he is not well known outside of those who follow politics. Consider that reality.
Next, he may be highly intelligent, but he is not particularly inspiring, and his presentation is sub par.
Mostly, the dems and media will mercilessly pound him as the focal point of the government shutdown a little while back. Those who closely follow politics will dismiss this point as negligible, but if you go back to my first point above, you must accept the fact that the overwhelming majority of voters do not follow the details of the whole story and have the “facts” (sound bites, jokes, half truths)impressed upon them from biased sources. He will never overcome this issue no matter how much Cruz supporters insist otherwise, and it will be what I believe to be an insurmountable obstacle to winning the general election.
Thank you Senator Dewhurst.