they don't have enough armor divisions to do that. Actually attack with everything at hand is what we should learn from AI! Individual battles may not end good in kill-loss ratio but the goal is break the line somewhere.AI should put all its armour in 1 army on 1 frontline and only attack with that. How hard could that be? That's O(1).
I did learn from AI spam attack and spread my tank into multiple tank divisions to attack multiple provinces on a front.