The reason why there is an explicit call out for surveillance on American citizens is because there are unquestionable constitutional protections in place for American citizens on American soil.
There is a strong argument that can be made that using AI to mass surveil Americans within US territory is not only morally objectionable, but also illegal and unconstitutional.
There are laws on the books that allow for it right now, through workarounds grandfathered in from an earlier era when mass surveillance was just not possible, and these are what Dario is referencing in this blog post. These laws may be unconstitutional, and pushing this to be a legal fight, may result in the Department of War losing its ability to surveil entirely. They may not want to risk that.
I wish that our constitution provided such protections for all peoples. It does not. The pragmatic thing to do then is to focus on protecting the rights that are explicitly enumerated in the constitution, since that has the strongest legal basis.