Quite possibly because the National Guard are FAR more likely not to fire on the general population; and why? because they are, most of the time, a part of the general population.
If the general population is preparing for war, as the scarcity of ammo, some firearms, and firearms-paraphernalia attests... then we should assume that the other side, our government, is also preparing... and that includes measures to alter the availability of those who know war.
Not to completely disagree with you, because you had the qualifier, "likely," but...
There have been quite a few times the Guard has fired upon American citizens. Waco, Kent St., and Watts come to mind.
5.56mm