There are TWO REASONS that Trump has the level of support that he has with Republicans:
1) His immigration policies are WAY AHEAD of the pack. Cruz is second, but he was still 6 months behind Trump in calling for large scale deportations.
2) Because of his immigration and trade policies, Trump can reach people that NO OTHER REPUBLICAN can reach (i.e., Independents and Reagan Democrats), as shown in this article and numerous other places. Cruz is locked-in with the conservative base and hasn’t shown any sign of moving beyond those people. The rest of the candidates will struggle to get conservatives (Carla, Ben) or drive them to a right into a Third Party (Jeb, Rubio, Christie).
Trump’s biggest problem, ironically, is locking down conservatives, who are turned off by his past. But picking someone like Cruz to run with will easily take care of that problem. For other candidates, they still won’t get the Reagan Democrats...and they also won’t do well with the base, no matter what they do.
I don’t know that Trump “looks down” at conservatives or that he is disgusted with the so-called conservative establishment like Rove, McCain, the consultants.