Who in their right mind wants to go to all that trouble just to elect a lame duck?
Republicans need a president who can get something accomplished in office. Only the threat of re-election to a second term gives force to a first term. That no longer applies in Trump's case.
He is a spent force who would be a mere place-holder.
By definition, anyone's prospects are better than his.
It would be a colossal waste of time and money to spend either on someone who has already been given the opportunity and come up short. If Trump were worthy of the office again, he would acknowledge that.