As a whole, why is it that Amanda and Elyot married Victor and Sybil?

Amanda and Elyot's previous marriage was too passionate and violent to last. Their second marriages are clearly an attempt for a calmer life, though this bores both of them enough that they run away together. While they do seem to care about their spouses enough that they are willing to help them do whatever it takes to get a divorce, Amanda and Elyot's feelings about their spouses are light enough that they are able to run away from the honeymoon with only a little guilt.