My thinking is that someone forgetting about a project, not caring about it, or for some reason being unable to update it (e.g. losing access to an account or even being physically unable due to injury or death) might not update the project to indicate this; I think a lot of the wariness of older projects that haven't been recently touched is because it's hard to tell the difference between "no changes need to be made so I'm leaving it untouched but monitoring" and "no one is even looking at this and if a change needs to be made, no one knows".