I though that this was just going to be an anti -sustainablility rant, but you bring up some good points (though not always very well! as many of the commenters here show with their counter examples).

Perhaps the value of photogenic desigenr tiny houses is to get people to question what they need, and how their lives are organised. As one person put it in parts of America they may be illegal due to zoning restrictions - and American zoning is notoriously unsustainable.

In Wales they have changed planning to allow people to build and live in low impact dwellings more easily without planning permission. This makes sustainable low energy lifestyles more accesible to many people.

Beyond tiny house for instagram, I see tiny houses as a way for people to question the way they live (as this article does) and perhaps question the rules or social constraints that stop them from living more sustainably.