The reasons are manifold, and have been detailed on this blog. The incompetence (changing positions, gauzy policy "statements,"), the hate (insulting John McCain, women, and non-Christians), and the self-aggrandizement. (Did Trump say he was more popular than Jesus Christ? No, but he could have.)
Large portions of the press are in the process of normalizing Trump as if he never said what he said. Trump's words are part of the record of his campaign for the Presidency. They cannot simply be wiped away. And here we have the incompetence of the press.
This level of candidate and press incompetence is a threat to the Republic. We cannot have such a shilly-shallying, weirdo as President. Incidentally, calling Trump weird is not my invention. Major Republicans have said it first.
So if "#NeverTrump" cannot get the job done, Republicans will have to come up with another way.
But the press must do its job.
Republicans Must Figure Out Way to Stop Trump