There's some logic to hiding the identity... don't know who/who's family to hack/threaten? But, you can just target the 2nd, or 3rd in command it'll be just as effective really.... so I'm not sure what the point is, besides some sort of security theater coolness.
The NSA is probably a bad example, given its entire existence was denied for two decades by the US.
The US has oceans on both sides, and the bureaucracy involved in getting airfare reimbursed for a bunch of agents is too much for most governments.
It's less the airfare than the fact that they would stand out. Fort Meade is a defence installation, people don't just "pass by". Most people in the area would have military connections and be wary of even-slightly-foreign-accented individuals suddenly popping up near critical areas or where heavily-protected personnel actually live.
That's not really apples to apples though. If we start bombing Indian reservations and trying to exterminate Native Americans, I'm pretty sure they would quite deliberately become a threat to American equivalents of this guy.
(...or perhaps I'm misreading you? not sure)
There have been reasons for folks to be motivated to attack personally the leads of the various American spy agencies over the last century, there really hasn’t been a significant amount of time where we weren’t in some kind of military conflict, very many of them with questionable to explicit human rights violations.
Sounds about right, but currently the American spy chief doesn't have domestic enemies. That guy does.
The head of Israeli intelligence is operating in a different threat landscape (both figurative and literal) than the head of the NSA.