I can't judge people about why their marriages break up because I'm not in the situation, thank God.
And a long time ago, marriage covered a multitude of sins - abuse, neglect, adultery - under silence, and the idea that marriage was supposed to last forever, no matter what, over and above whether or not people were actually happy. So for some of those unions, divorce is NOT the worst thing that could happen.
But, since that secrecy shouldn't exist anymore, I do think part of the problem today is that people don't think long and hard before they get married in the first place. They marry people because they think it's time to get married...because they "want babies"...they want a big wedding...they're tired of being alone...because it will change the other person...all kinds of reasons, none of which have to do with the idea that the person standing in front of you is who they are, they're not going to change and you want to spend the rest of your life with them! People don't THINK.