Right but I'm saying that's what their standard MO was when a system was deemed lost. At that point, nothing more could be done, so nuking the system wouldn't cause anymore loss of resources than leaving it to the Flood since there is no such thing as taking a system back from them without burning it to the ground anyway. It would only deny them resources, which is basically the only way to slow them down anyway so what would be stopping the forerunners from doing it exactly?