[trowawee]

I sorta feel like you answered the question in this comment, despite saying that you don't have the answer. The answer is because you want to stay in touch, because humans (mostly) crave contact with other humans. Loneliness is endemic in a lot of places right now. Many people feel alone, and many people feel like they are "bad at staying in touch", and maybe a tiny handful of people are naturally good at it (altho in my limited experience, the ones who are good at it are usually using some system, even if it's not quite this technical).

Personally, I use Monica and regularly make lists of people that I want to stay in touch with, and then periodically go through those lists and reach out to them. It doesn't have to be a huge personal missive, just a text or an email that says something like "Hey! I was just thinking of you. How are you/you and the family doing?" If something more deliberate triggered the desire, I include that. And it frequently triggers conversations that, like you experienced, were a lot of fun, and end up actually feeling energizing, rather than draining.