As far as the origins of the Seven Deadly Sins go, the movie provided a reasonable amount of background on them, so throwing in a little extra for the Young Sivana might have been too much.
While Thaddeus Sivana being brought to the Rock of Eternity via an elevator is reminiscent of how Billy Batson was brought there through a subway train, the car crash was definitely the more jarring approach, as initially it looked like the Sivana family avoided being struck by one car, only to be hit out of nowhere by another.