Edited for grammar
Additionally, technically there are two other requirements before committing treason causes a loss of citizenship, just as with all the other potentially expatriating acts: the treason must be committed voluntarily and with the intent to relinquish citizenship, as judged on a preponderance of the evidence standard (i.e. more likely than not). This is a court proceeding and the claimed loss of citizenship can be challenged, though of course those requirements are more likely to be satisfied in treason cases than in some of the other potentially expatriating acts.
None of this is consistent with a unilateral military strike.
It's much easier to kill you and then say that you and your estate have no standing to challenge the official story to see if you were on a list because only people who know they are in the list can see if they're on the list.
If you read the applicable provision of law—8 USC Sec. 1481(a)(7)—you have to not only commit an act of treason, but do so “with the intention of relinquishing United States nationality” in order to lose citizenship.
As long as you still want to be an American, albeit a traitorous one, you don't lose your citizenship just for being a traitor.
(And, it also requires conviction of the treason by a court martial or competent court, so if the government wants to give effect to this, it literally not only have to get a hold of the person, try and convict them of treason, and then prove additionally the intent to relinquish citizenship. At which point the last bit is quite likely to be moot.)
No.
> Why not at least go that route, vs blatantly killing citizens?
Because it doesn't exist, and if it did exist it would almost certainly be a contested judicial process which would bring in the same problem as criminal prosecution of enemy combatants that happen to be US citizens but are physically located in territory not practically subject to US or cooperative jurisdiction.