Maybe I have seen too many movies and have too much faith in the competency of our intelligence agencies. But, I expect that there is a high likelihood that there are foreign operatives who are embedded as employees at Mara Lago, or who have some sort of access greater than that of mere 'club members.' Since I (an internet moron) can easily foresee that circumstance as highly likely, I would also think that our intelligence agencies have similar concerns and have our own operatives similarly embedded. They saw the shit Trump pulled in Helsinki in 2018 and know he is an ongoing risk. Alternatively, we must have some type of continuous surveillance of what is going on inside the walls in all areas at the club if there aren't embedded people.
If my assumptions were true, it seems likely that we have folks (beyond MAGA whistle-blowers) who already know what Trump was doing with those documents, and know what he did with the ones that have been unfoldered. The feds already know what he was doing. If those answers are never publicly disclosed, it must be worst case scenario and they have determined it is information that the American public cannot handle.