Because Trump is too conservative then. My only quibble with your statements then is that I wouldn’t label those Pubs as “moderate”: RINOs (and worse) would be more accurate labels.
And Trump isn't "too conservative," either. He's nothing except all over the map on any given issue. He has no political principles and operates for his own self interest. Most of his support comes from people who like him for what he is not (a career politician) than for what he is (a businessman and entertainer).
There's nothing wrong with that, but let's not overestimate what he represents. I suspect most people who vote for Donald Trump in an election would be perfectly comfortable voting for Ronald McDonald, too.