I would say previous presidents would have been trusted with all the intel of the highest levels of classification, but Trump is a bit too uncouth and unhinged to be trusted with the worlds biggest secrets, so they wouldn't tell him a thing. Especially after that 'drain the swamp' promise to which many in the political establishment enjoy laying about in.
As for the government being successful covering up the truth of the flat earth, it is only doing well because from birth we are indoctrinated to believe in the globe. For my sons Christmas I will probably buy him a globe of the Earth. I feel dirty to do it but he seems to like it. Probably because it looks like a colourful ball to play with, but his brain will be forever wired to associate the Earth as a ball. It is damn near impossible to break this conditioning. That is why even when the political establishments screw up in this regard, no harm is ever done.
If you want a case in point. Look at John Davis. A flat earth champion who is recently in a book but under a title of 'radicals'. When in actual fact, it should be 'radical' to be believing the Earth is a spinning ball, zooming around the sun at fantastical speeds