Their reinforcement rate is probably higher than the attrition rate, assuming that the armies are over the supply limit. You won't see the impact in the individual armies, but their manpower reserves are taking a hit.
To lower your attrition, get generals with high maneuverability and split up your armies until you're ready to battle. To increase reinforcement speeds, move your domestic slider towards Quantity or hire a Quartermaster.
To lower your attrition, get generals with high maneuverability and split up your armies until you're ready to battle. To increase reinforcement speeds, move your domestic slider towards Quantity or hire a Quartermaster.