That isn't wrong! My original plan was to design a separate set of levels with obstacles for single-player (such as the level with 4 diagonal saws moving about), but I ran out of time.
Though the challenge in single-player on other levels is largely self-imposed, with ever-growing speed you do reach the point where you can no longer just bounce the disk back and forth at the same wall as the disc comes back faster than your weapon cools down.
As for reason, your score is the amount of times you've managed to hit the disc before it killed you, so there is that.