How come malphite passive is the first shield to break?

So I actually like for his simplicity and all that,went support with a 5 man and noticed shield battery is under malphite passive,so when malphite is hit his passive goes down when he is shielded by targons brace. I for one find it kinda sad after maplphites new changes,where if his passive is up his armor passive from his W triples,going from 10%-30% to a 30%-90% I for one like the change. specially when I have 110 armor before I buy any,and gives 36 extra armor.amazing when you go ,an MR item then later get like 600 armor for initiation.