I recently went through a Docker Pluralsight course that made extensive use of this removed feature. I can scarcely imagine the politics behind this but it makes things much more confusing and the third party open source tool people recommend to replace it is difficult to use and doesn't provide the same information.
Part of the reason for removal (beyond just being difficult to maintain) is it is tied to the (now old) method of image storage where images were all just a tree of layers and any layer is considered an image even if you can't actually run that layer.
Today images are flat. You have a proper thing that is an image and and image is composed of layers. Some images may share layers (so they only need to be downloaded/stored once) but there is no hierarchy. You don't see layers anymore except by inspect an image (and even then only the content hash).
There are quite some reasons for this to be the preferred method.
