Another reason--not the only reason!--I like to preserve friendships is because they're a really interesting source of entropy. Isolated living tends to be pretty consistent, predictable, boring, etc., but you never know what ideas or events or connections a friend may introduce. I think about the butterfly effect, of how a single interaction can set us on a completely different and often unexpected trajectory.
If I hadn't stayed after church for an optional members' meeting, I may never have gotten to know Ariana, who would eventually ask if I wanted a ride back to Michigan in the early stages of the pandemic. So I probably would have been too cautious (read: lazy) to travel home, and therefore spent the spring and summer in Cambridge instead of with family.
Or if I hadn't started catching up with Peter, I may never have thought to buy a volleyball net system. Which has in turn branched and spiraled off into countless other interactions with people I wouldn't have ever talked to otherwise--Vivian, Ivan, Ruth, Catherine, and a whole lot more.
It makes me curious about the ripples I leave in other peoples' lives. Most recently, I referred a friend to Commure--they just accepted the offer over Amazon last week, and I really hope they enjoy it here.