Any American should represent their country. Any American working in any govt should be aware that they are representing the US.

When you have the honor to be chosen to be part of an international institution, you're expected to represent it.
It's exactly like the European Commission. The commissioners very often have to rule against their own country and that's what happens.

If somebody coming from Lockheed becomes a NASA representative, he is no more expected to work for his former employer.

It's a matter of ethics.

Unless of course there is no such thing as ethics in your part of the world.