That’s because the SPAA is considered a vehicle and is mobile. It takes damage from larger caliber weaponry but none of the armored parts take damage from small arms fire.
Personally, I don’t think it should be disabled like the (H)MG nests. Its a much larger weapon and should not be damaged by small arms fire. That should be one of the POSITIVES about it.
Keep in mind you can still shoot operators off with small arms fire just not the weapon itself.
This would be to keep balance and keep things like AT squads relevant.
- Look at the HMG nests for example. When they originally came out they required an AT squad (or tank shell/ explosive) to take out. Tons of people started using the AT squads again and it helped to diversify the squads used.
However, after they nerfed it and made it only take a couple small arms bullets, the usage of AT squads SIGNIFICANTLY dropped. Instead, all the spam classes got even more popular because it no longer took anything special to deal with them.
THIS is why I suggest not letting small arms damage/ disable the updated AA/ AC.