In reply to James123:
It's the way most down clothing is made too. I guess they could box wall for synthetic down also, but cost is clearly high for that construction.
It's an odd thing, it is not the case that stitch-through simply doesn't work - this jacket does keep you decently warm, just like the stitch-through down jackets I've used. But it's clearly not as efficient as it could be, but perhaps even despite this, it's enough for most people? And people don't want to pay super high prices for box wall jackets?