Cascade is a multifunction ability. Since the duration starts when the wall stops moving, a longer duration benefits it when used to block or isolate an angle, but is a detriment when using it to push through a chokepoint (ex. Either path to A site Fracture), since you will now end up pushing past it before it goes down normally, or have to get closer so that it stops at or past the far wall.

Since changing the distance it can travel would have adverse side effects for balance, letting us end a cascade early would resolve the problem without introducing new range or power in unintended areas.