Less for the fact that we miss every now and then, but for the fact that if your shotgunning or fusion rifling, the distance from you to the special is a few steps. But if you sniping and run out, usually you get killed on you way there, or someone else on your team gets the ammo before you can.
It just slows the pacing when you have to walk around looking for special.
maybe even if the special didn't even drop, it just loaded into whoever got the kill, so if your an extremely talented and skilful titan that shotguns people with incredible precision, or a sniper, you can keep a streak going without pause.
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What needs to happen is snipers automatically pick up ammo on headshot kills, this promotes skill and lets players not have to rush for the special ammo. Shotguns are on every corner, I feel your pain in running out of ammo and then getting wrecked