there is many reasons why people add eachother, they like you and they want to track you/see your activity or see where you are playing easily so they can join you. if they dislike you over time then they would remove you since they dont care about where you play anymore. it shows all of their registered names of the friend or fanboy/girl who added you. I think this is as simple as i can explain

some people like to see their fan list go up just like they like seeing their rate go up. is the other reason