User blog comment:B214/Question and Answers 3/@comment-69.60.247.47-20140712025508/@comment-16281343-20140712034830

He was sick. That may have contributed on to why there's only 2 images for Volume 18 but that's probably not the main reason.

You can see the decline in numbers of image in the past Volumes. As to why? We have no idea.