Shipping has always been a strong point for Ikea. Just look at how efficient most of their stuff is packaged, usually into very neat rectangular packages. They can fit a ton of stuff into a small volume, which improves shipping cost a lot. Last mile will always be relatively expensive, but shipping a truck load or a 40ft shipping container is relatively cheap. In the end it all comes down to cost per unit of volume, compared to the raw product cost per volume. A dense product will not nearly be affected by high shipping prices as much, and due to Ikea being insanely good at packaging, I expect they are outcompeting the rest of the market at this game by a decent margin.