The marriage vows often include the line  "for richer or poorer, for better or worse".  It seems that even when it's so bad that a divorce is inevitable, the "poorer" part kicks in and keeps people together...at least according to YourTango.com

Experts say that poor economic situations cause tension in marriages, which ultimately leads to cheating. However, despite the infidelity, couples are staying together -- likely to avoid the financial woes associated with divorce and the division of assets. Cheating has also become easier, thanks to dating websites like AshleyMadison.com, which lets married people seek out other married people for secret affairs. According to the CEO of the site, Noel Biderman, users openly admit that their marriage is over and they're just riding out the economic storm. (YourTango.com)