It's because it's broken per initial information... you should get enough ammo for 2 kills... so it should be 6 for BB... fusions should get 2. As far as I know, they haven't commented publicly on the issue. I think they should move to ammo crate, because it's a much easier system to manage. Mercules talked about it... with ammo crate they can tune the ammo drops per weapon... they can't do that with the transmat system. And from my experience, though limited, I like ammo crate better... it promotes dueling and earning your ammo in a better way than transmat... If you use dbl primary you can still benefit from ammo crate... by stealing the crates defensively... even if you're not using the ammo.