Why is the lunge mechanic designed the way it is?

Genesis219

To elaborate my question is why during a lunge as a killer are you able to back up during that action? The definition being "a sudden forward thrust of the body, typically with an arm outstretched to attack someone or seize something" it seems odd to me (hopefully this doesn't sound like me complaining) I'm just genuinely curious as to why you'd be able to back up while performing an action that I imagine would be a full commitment to launching yourself forward into a strike/swing. Thank you in advance for any answers offered