The simple fact is a false start is a movement that, by definition, is BEFORE the play begins. If the play has not by definition begun, and the foul is committed, how can there be a play?
In regard to illegal motion or illegal formation, those are legal UP UNTIL the ball is snapped... so it is the very start of the play which makes those situations a penalty, hence you can continue... but if the penalty happens BEFORE the ball is snapped, before the play starts, there simply is no play to continue.