The same reason our other few trolls do, they can receive a form of attention here without stepping away from the pc and leaving the safety and security of their mother's basement. The responses they receive, even if negative, are seen as communication and in most cases the individual is unable to effectively communicate in the real world. Just a glance through their past threads and posts indicate the level of mental/psychological deficiencies they are burdened with, the bantering within these threads make them feel that they are part of a group, something they have likely never felt in real life. Sad.