Suppose North-South ("N-S") has a combined hand that can make a contract of 4 Hearts. If they win 10 tricks and make 4 Hearts, then they get 120 points whether they bid 4 Hearts and made game, or (say) just 2 Hearts and made 2 overtricks. Sure, points from the 2 overtricks are Above The Line, but so what? If fewer points are Below The Line and more are above, it just means that they get to play more hands before they accumulate enough points to win a game.
Also, by bidding below game, they reduce the risk of not making contract. If they win only 9 tricks and make only 3 Hearts, then: if they had bid 4 Hearts in the first place, then their opponents get 50 points and N-S gets nothing! But if they had bid only 2 Hearts in the first place, then they still get 90 points (30 of which are Above The Line). So why would they try to bid 4 Hearts just because the Below The Line points happen to exceed 100?
After all, it's the total number of points that counts. If their opponents quickly win many points Below The Line and achieve two Games, bringing the Match to a close, that's not necessarily a bad thing as long as N-S has more total points when that happens.
This question is Rubber Bridge. I am asking whether there is some other scoring about which I don't know, which gives an advantage to scoring a whole game at once. For example, is there a bonus score when a team makes Game (ie. 100+ score Below The Line with a single hand)? I know there are bonuses to making a small or grand slam. Are there game bonuses with other types of contract bridge?