The Quran says Allah is oft-forgiving so there is divorce for couples who cannot get on, why live in pain and suffering with someone you do not love or like? When they are divorced and they feel that they have made a mistake then the Quran says they can re-marry. But forgiveness is only for genuine mistakes and not deliberate actions done over and over again.
Hence, marriage, divorce, re-marriage, divorce, re-marriage, then a final divorce is allowed for the same couple before it becomes a mockery and the requirement to marry another man is there to put a stop to this; If you cannot work out your differences in a third bout of marriage, then you should know that the only option after another divorce is a GENUINE marriage to someone else. Fix it, or lose it!