They don't have the strength to be buried. All of the strength is vertical in the corners for stacking. Once you cut into them for windows or more doors, you greatly reduce any strength. By the time you get done modifying it, it will cost more than traditional building materials.
Another unmentioned problem is that the plywood floors are saturated with carcinogenic insecticides- and not a small amount. Source: I sealed floors for a container reuse project.
(i like this dream, but it just isn't practical)