It's probably more about convention and terminology. Security researchers tend to label foreign actors as APTs partly for tracking and reporting purposes. With domestic agencies, especially US ones, there's either reluctance or it's treated as a given.

Sure they are. https://en.wikipedia.org/wiki/Equation_Group

Remember the Snowden leaks? They are.

WTF is an APT?

Advanced Persistent Threat. It's a cyber security term.