Why doesn't Trump just declassify everything now?
The same reason that other loyalist insiders haven't done so. If you strike at the enemy, expending your ammunition and announcing yourself as a critical threat, but you don't utterly destroy him, then he will desperately strive to suppress your message and kill you and your associates.
If Trump reveals the globalists' crimes, losing his blackmail leverage, but he doesn't destroy them because the American people simply aren't paying attention, the globalists will subvert the courts and counterattack. This counterattack will be all-out, suicidal, desperate and cause extreme collateral damage.
That's why Trump has spent so much effort ensuring that everyone, both in the USA and across the world, is watching this season finale. So that when the truth is revealed, the massive shift in public opinion shatters globalist morale and forces capitulation.
If you think this is theoretical, remember how popular Obama was and still is. Consider that the collateral damage will include relationships within your own family. Perhaps it already has.
This is not a game. Communist revolution often ends in gulags and mass graves. Mass casualties are expected.