well, when we did the drill, we landed the foot in front, then set it back.
So we don't get into the habit of not closing in, or not following up.
and to work on the follow through.
If you always set it back, it becomes a bounce off.
It's not a bounce off because of the stance switch between the kicks.
Also the exercise is for speed and coordination. It's not supposed to encapsulate the whole fighting strategy.
But since you mentioned it a kickers best weapon is control of the distance so landing back is just as important as landing forward. Note also there is a side stepping variation...