Why do people want to hold onto something that was never there?

Hey look....it's only been a month this time...I'm almost a proper blogger now....well not quite....

So, kind of following on from my last post but with a different person this time.

What I am wondering now is why do people who haven't been in touch for over a year decide to randomly get back in touch?  What is it that motivates them to get in contact again when there hasn't been any kind of relationship in the meantime?
Now I'm not talking about an old friend where we've just lost touch, I can understand how that might happen.  I'm talking about when both parties have decided that the relationship should end in the form it was in and then not be in touch following on from that time.  As I said in my last post, if we weren't friends before why would we suddenly be friends now?

It's just not something that I would do so I'm left a little confused.   I suppose for me when a relationship ends by choice then it's over.  We either stay friends or we don't, and if we don't then why ever get back in touch?  Yes that person had an impact on my life at the time but I haven't thought about them since so why would they think about me?

Maybe I'm less sentimental than other people but there are so many people in the world, when a relationship breaks down I re-assess, learn from it (hopefully!) and move on.  Why would someone want to go back to someone with whom it didn't work?  There are so many other people out there to meet and be in relationship with.  I just don't understand.

Answers on a postcard please :)