How long has Cruz been in the Senate? What has he accomplished other than blocking its work on every topic? Which relationships has he built? You're not naive enough to believe Cruz's and Trump's rhetoric that one can rule a country through willpower alone, do you? No one will work with Cruz and Cruz won't work with anyone.
He's not knowledgeable enough to hold any positions, and he doesn't have the right advisors to make him informed. Just how easy do you think being president is? You need to know how politics works. You need to have experience running a political system. You need to have the ability to build and maintain relationships. You need to know how the government functions, how people function within the government, and how to get things done. This isn't enough you magically learn on the job. Look at Obama's mistake. Half of them are a result of political inexperience. And you'd replace him with someone who has no experience at all?
Bush and Christie are polling at under 10% combined. Trump is up by a good 25% over Rubio.
Edit: compare Cruz to someone like Paul Ryan, someone who's about as right-wing as Cruz. And yet the guy has the respect of his colleagues, both Democratic and Republican, and manages to get things done. That is what being a politician is about. Promoting one's agenda, but also getting things done. Empty rhetoric doesn't help anyone.