Accused persons are frequently advised not to speak to the police or the prosecutors, except in the presence of their lawyers, prior to the trial. This protects the elements of their defense from the prosecution developing specific counter evidence or arguments prior to hearing it for the first time in court.
It is forced to build its case on the evidence it can gather independently. Sometimes this is very difficult and results in a decision to reduce the charges to what can be proven or to a decision not to prosecute the case at all.
President Trump‘s lawyers are simply exercising a common defense strategy to protect their client during subsequent legal proceedings.
The president, his attorneys claim, doesn’t require any other government official or procedure to verbally pronounce a document declassified. He is, by authority of his office, the highest classification/declassification authority in the government. The challenge for the government is to prove that an order given given by a sitting President to Executive Office of the President subordinates that all classified documents being packed by GSA for removal from the White House to Mar-a-Lago (sp) were declassified is, in fact, inadequate to accomplish the declassification action. In order to do that, the government would have to prove that the president lacks the authority of the chief executive. Not sure if the government even wants to go there in pursuing this case.
It doesn’t matter if the order was improperly carried out. The issue is whether or not 1) the president was competent to give the order; 2) that he still was President at the time the order was given, and 3) whether or not subordinates improperly carrying out administrative procedures to mark the documents as declassified meet the elements of the offense for the serious allegations (treason/espionage) supposedly being made by the government against President Trump.
They have not submitted any evidence that President Trump verbally pronounced the documents declassified in the first place. That's what is so odd. If you want to make the argument that the president can declassify documents anytime he wants with just a word, that's fine. But you still have to introduce some evidence that he actually did do that.