Why do people ignore your friend request on Facebook, only to accept it 6 months- 1 year later?!!?

Hi I have added a couple of guys I liked on Facebook, only to have them not accept. However 6 months later (first guy) and even 1 year later (2nd guy) I get a notification saying they've accepted!!? Why do people do this? Obviously they're not interested, otherwise they'd accept right away, but why ignore it only to accept ages later?