I have been following a youtube couple building a shipping container home. It isn't as simple or cheap as you think. You need to deal with rust, sealing floors that have chemicals, cutting out windows, etc... I wonder if they can do that only because they live somewhere with no building regulations.
In contrast to that, our local school additions were a snap. They were prefabs that just needed to be dropped onto slabs.
I think there is a definite hipster trendiness to some uses of containers. It's the typical hype, trough cycle where it's being used in novel ways but also not so good effective ways in other cases.