, because you are supposed to understand the oath,
Article V is the only way to defend the constitution at this point.
http://www.military.com/join-armed-forces/swearing-in-for-military-service.html
The Oath of Enlistment (for enlisted):
"I, _____, do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; and that I will obey the orders of the President of the United States and the orders of the officers appointed over me, according to regulations and the Uniform Code of Military Justice. So help me God."
When people have to file lawsuits like this,
http://www.foavc.org/reference/doc4.pdf
It's clear that citizens and Article V are going to be the only defense. And soldiers have had lots of opportunity to discuss this, a lawful and peaceful defense of the constitution, but they can't. They are too afraid of command.
http://algoxy.com/ows/soldiersinquiry.html