Short answer: Because materials are expensive and a great knife takes a long time to make, and we can only make so many per year.
Longer answer: Knifemaking combines a wide range of difficult skills, from understanding metallurgy to fine woodworking to leathercraft. Learning to do them well can take years of dedicated effort. Learning to do them well so that they are also works of art takes even more.
As with anything else, that knowledge doesn’t come cheap. And the equipment needed to use those skills–anvils and tools, hydraulic presses, heat treating kilns, grinders, forges, drills, and saws–also represents a significant investment. We use the finest materials available–from exotic pink ivory wood and gemstones used in our handles to high-end steels such as Apex Ultra. We recover those costs in the price of the knife.
A Nathan Cline knife takes about 40 hours to make, start to finish, not including design time.