The problem with wooden domes is that plywood and other sheet-based building materials, in the US, come in 4 by 8 foot sections. You end up wasting a lot of wood to make a dome. Building with earth solves this problem.
It’s also beautiful. Earth building offers the opportunity to do more graceful forms than can be accomplished with sheets of plywood. The example Kurt linked to is a house built by Simone Swan. You can see more photos of Swan’s house at the Adobe Alliance.