The national guard is expected to be near combat ready so it can serve as a second line/auxiliary force in a hot war. Like it did in Iraq and Afghanistan - although more often than not Guardsmen saw combat.
You put women in a guard infantry/cavalry/tank/arty unit they are going to fucking eat up training time, every fucking little thing will become an EO complaint that will involve the AG, big army and possibly the state government and law enforcement.
If you knew anything about guard combat units you know they only have a short amount of time for training, will sleep less than 9 hours total during a drill weekend.
There are a whole shitload of other constraints as well - in the active army Female grunts can just be shuffled in to a desk job, taken off the line completely, be a TOC bitch, or even be forcibly reclassed - needs of the army and all that. The guard doesn't have that luxury