Because they will only support someone who turns the blind eye to the fact that Planned Parenthood does things other than abortions, turns the blind eye to the fact that the Iraq war destabilized the middle east, and turns the blind eye to the fact that George W. was a terrible president who lied about Iraq having WMD’s.
In short, some people would rather just blindly follow the GOP establishment. Some people are liberals and therefore Trump lost them at “I’m running as a Republican.”
I’m not going to bother addressing the absurd conspiracy theories that Trump is a secret liberal running as a Republican. If you buy into it, put on your tin-foil hats and go back to your bunker.