There are a lot of mismatch in "marriage". A lot of us don't know who fit us when we were young. When time goes on, we grow up and start to know more about who we really are and what we need.
Western people often choice to leave the broken marriage and move on to the "greener" prairie. Out Chinese tend to chose stay for the sake fo children, family, finance, etc. In a collective cuture, divorce has more to lose for the parties involved.