Because Republicans don't want John McCain.
McCain hasn't one primary or caucus amongst "Republican only" voters. It has been Indy's and Democrats that have given John McCain his three wins in NH, SC and Fla.
If on the other hand he actually wins the nomination, then face the reality that not all republicans are conservatives. While they are still republicans. That conservatives do not own the republican party, and cannot require whatever they like of its members.
Did Bush change his mind on immigration and agree with you because you stomped your feet?