Some people just need to get it out of their system
Maybe they don't like to burden their friends and family with their problems or maybe they just want a new perspective since their friends and family would only give the most optimistic response and not always the hard truth.
If you discuss your personal life online, you don't have to hide certain things from your family and friends because people don't really know you in person online.
This maybe a Naruto forum, but there are still other sections of NB where people discuss other subjects like in the "chatter box" and "general discussion."