Even if it doesn't kill them, thick smoke in the cockpit is obviously going to impair pilot performance, and that's a big problem when it's most likely to happe

Even if it doesn't kill them, thick smoke in the cockpit is obviously going to impair pilot performance, and that's a big problem when it's most likely to happen during the most dangerous phases of flight (takeoff and landing) when they already have a lot to deal with. It seems strange to ignore it when the risk could be mitigated with a simple change of procedures.