Why has this been ignored?

"The Supreme Court does have the final voice in determining constitutional questions; no person, not even the President of the United States, is completely above law; and the president cannot use executive privilege as an excuse to withhold evidence that is 'demonstrably relevant in a criminal trial." - Holding in United States v. Nixon (1974)

"Neither the doctrine of separation of powers, nor the need for confidentiality of high-level communications, without more, can sustain an absolute, unqualified Presidential privilege of immunity from judicial process under all circumstances. The President's need for complete candor and objectivity from advisors calls for great deference from the courts. However, when the privilege depends solely on the broad, undifferentiated claim of public interest in the confidentiality of such conversations, a confrontation with other values arises."
— Chief Justice Warren Burger from the Majority opinion.