[Groxx]

It's covered explicitly in the "goals and principles" section. They're aiming for a reusable environment for older games, not a single-purpose one.

[jayd16]

They could make a base image and then an image layer that contains the game files only. Now you have a single file image per game with a consistent base.

[Groxx]

Sure, as a follow-up they could do that.

That's (very clearly declared to be) not the goal of the author though.

[jayd16]

My point is that by separating the layers it does fulfill the declared goals but in a more portable way. As implemented, there could be hidden dependencies on the local file system or across game installs.

[reificator]

But it then prevents redistribution of the container images in a legal manner, because the game files themselves are still under copyright.

[djhworld]

I guess one concern might be the author wanting to push the images to a public repo so other people can use them - which would probably get the author into a bit of trouble for distributing paid content.