Friendship Rot

I may not be the first, but I have noticed something on social networks that hadn't occurred to me, although it should have, if we have link rot, why not rot in the relationships between friends? I've noticed on our farmfoody.org site there are some lapsed users, since their email addresses are bouncing. It occurred to me that they still have friends but no longer participate in the site. These are ghost relationships suffering from what could be called friendship rot. I suppose Facebook must have millions of people who no longer participate but have accounts and friends. It must have a terrible friendship rot problem. I suppose this form of relationship rot extends to LinkedIn and other sites that depend on navigating networks of relationships between people.