There’s a good reason why the FBI might not ask the NSA: It is advantageous to the FBI to set a legal precedent here by forcing Apple to cooperate. If the FBI had won this fight, it would’ve had a strong precedent for conscripting tech companies to assist in dismantling their security in the future
This, This is why the FBI wants to make Apple say UNCLE, to have a precedent to force anyone else to do what they want