There is some basis for it. If someone actively and aggressively wants to stab you you should have your weapon drawn. But the training seems to be around assuming everyone within 30 ft wants to stab you.

I know that's the training. What I've read is that there is no basis for that training. Do you know of the basis?

Trying watching videos of the Tueller Drill.

I've done it myself, timed the speed I could lunge 21 feet, it's true enough. And that's a minimum, allow more feet to realize there's a threat etc.