Why don't you enlighten us?
An Executive Order is issued in order to put laws into effect, or to execute policy within the constraints of extant law.
EOs are scrutinized by the White House Counsel's Office to ensure that they do not violate the law. EOs frequently need to be changed because the underlying law is changed by Congress.
This is why we had a Marine O-5 running covert operations in Nicaragua, because Congress forbade the government from spending money to support the Contras, and any effort to do so via executive order would've been shot down by the White House Counsel.