Why do interest groups exist?

group exist to have a sense of belonging and to reach the same goals.Some types of groups are social group,family group,secondary group,primary group ,social catergory and others.It have formal groups and informal groups,formal groups are will organized and informal group lime on the block,like pe-pressure but fomal groups are better and you get great qualitys too.Also congergation group, tempory group do not stay together they just go to do something and for a specific reason.  more