Because Trump is very likely to lose.
Even if we had a squeaky clean, articulate, solidly conservative candidate without all of Trump's baggage and negatives, the tipping point came in 2008.
As a country, we will never again elect a candidate that doesn't promise free stuff to everyone.
The takers are in charge now.
Trump is a Nationalist closed border and anti “Free(Rape) Trade”. That is why you don’t like him.