I personally think it's that he has absolutely no clue what he's talking about so, either he realizes that or people around him have realized that and told him to shut his mouth and don't say anything about specifics. They had to throw something out there, so the easiest thing to do is just say...."We are going to drop the corporate tax rate to 20% and give everyone the biggest tax cut in the history of the world."
He would have absolutely no clue how to talk about specifics and if he did, it would look like the Roy Moore representative interview with Jake Tapper.
So.....Funhusker, is right in that he will trumpet and sign anything that comes to his desk written by Republicans.