Why did theyIn Primordium,we find out that ancient humans didn't find a cure as the Forerunners had though, but the Flood simply chose to stop infecting them. It could still theoretically be possible that there's an actual cure of some kind, but there's been no indication that anyone ever has fund it, or ever will.
choose to stop infecting them? What? I thought the Flood didn't have motives otherwise :|