I think that the reason is that: In todays world the indivisual identity has reduced and even from the time of our birth we belong to some groups which we dont even have advantage to choose. The world has reduced itself to gaint indivisuals that has collective intellegence of hundreds of people which make it almost impossible for an indivisual to survive. So people believes that has to be in a group, for having special advantages, like safety and strength.
I don't know why people create clubs. My friend joined a club and they wanted to know where he LIVED. Anyway he gave them a fake adress.. But I also think it's just to get APs in some kinda way and making their own forum. Anyway..DON"T JOIN CLUBS! THEY WILL ASK FOR PERSONAL INFO (sometimes)!!