Also, part of the original idea of using bleach/ammonia was that it was cheap. It was quick murder on a budget, (I originally got the idea during a shadowrun game to counteract the overly engineered overly expensive synthetic shit they had). Bleach was just cheaper. These are all far more effective, but it's just, ya know, cost and availability. Highly concentrated pool chlorine and liquid nitrogen for example can send people into a come in like two or less minutes, but it's having quick access to liquid nitrogen. you can plan for it, but you just gotta hope that no figures you out.
Also, again, price
Edit: Correction, liquid nitrogen and pool chlorine don't actually do anything together