Because a poll is selective and can't register the minds of the individual voters in a county. Every state and national election is determined county by county.
When Cruz ran for US Senator, the polls said Lt. Gov. David Dewhurst was going to win, down to the day before the election. Cruz won handily because he was able to contact individual Republican voters in every county and they went to their precinct polling place and voted for Cruz.
That is what you will see happen in the caucus of Iowa, and primaries in every county in New Hampshire, and all other counties in the US.
Have faith Cruz knows what he is doing and has the money to have workers, volunteers and paid, in every county in the country. Every election for state and national candidates are still local. Think about yourself. You live in a county and have a precinct polling place. If you voted in the last Republican Primary, you get personally contacted by a candidate or candidate's worker and the candidate's positions are explained to you, plus you get fliers very often from the candidate with his/her positions in print.
Then, just before election day, you are contacted again to remind you to vote and if you don't have transportation, a worker will come get you and take you to your polling place. That is how a Cruz election happens and the way it happened in Texas. I think it will also happen in every county in this country 'cause Cruz workers will be in every county.
That is a superb explanation of how it is done by the grass roots.
So the senator will leap frog from 8.3% to over 22.3% for the real-estate mogul in Iowa! OK!! This will be worth watching.