I can think of one.
If it were moving and/or shooting at a moving target it would need that rate of fire to have a chance of hitting something and doing damage if it did managed. The Time On Target could be minimal.
And it's not as if there isn't the capacity to carry a lot of ammunition.
OTOH, it can only point one way at a time. I'd like to be about anywhere but in that vehicle unless it were moving away fast. It will be a very high priority target. Purely a defensive weapon.
Arf