system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why the facebook chat list is structured that way, and why people I haven´t speak with in years are located near the top?
gpt
Facebook developed a very complicated algorithm to determine who you might want to talk to. It takes into consideration many things such as the friend's activity, what you have in common, locations and checkins, events, common friends, profile visits, mentions and tags, etc. 

The exact details are known only to Facebook's developers and are not publicly available.