I’m not choosing to go unarmed against a knife wielding person. The idea is that I don’t always get to choose. No one can maintain a constant reactionary gap and perfect situational awareness at all times.
Ideally, I wouldn’t be there. Or I’d use a gun. Or a flamethrower. Or even sticks. This is a set of skills for a specific scenario, not the only thing in my arsenal. I can add the knife control techniques to things I’m already training.