Eight of them does not make for none what so ever, by the way you didn’t count the Air National Guard units and the Marine reserve units, or for that matter all the reserve officers that were sent to Viet Nam.
Most states have more than 8 of their units called up for Iraq alone, so the number of guard units called up for Vietnam certainly paled by comparison. The fact is undeniable that during Vietnam the chances of joining the guard and going to war was next to zero, while guard members during the World Wars or the Iraq wars had close to a 100 percent chance of going. Quibble over semantics all you want, during Vietnam the National Guard was the branch of choice for those who couldn't avoid going to the war through other means.