There are people who fade out of one’s lives for various reasons, but it doesn’t mean that the relationship has to end at that. There are many schoolmates, coworkers, etc. who I wish l I had some idea where they were now, which I don’t have right now because of my general avoidance of social media.
This is just a way of keeping on the pulse and generating common context if said pair were to meet again, instead of simply awkwardly smiling and trying to end a conversation as soon as possible.