As long as Trump holds onto the documents and keeps them out of reach, they create leverage for him. Hes using them right now to terrorize a lot of very evil players.
They know he knows.
He torments them with noise about being set to release *everything*, generating mass histrionics. Then he walks it back. Never mind.
Do that a few more times and some of them will crack.
Spilling it all now also becomes a gift to defense counsel. They learn exactly what they need to cover up well in advance of any prosecutions.
Granted, were all frustrated and want action this minute.
Its much too early in the process for the President to shoot his entire wad.