How do you smelt uranium? Why is it harder to produce than other metals?

Uranium is very rare compared to most elements, and it forms slightly unusual compounds compared to most metals. So some special chemical processes are used to extract it. Most of the basic details are at the link below.

It's also harder to produce because of issues with radiation safety, so facilities have to handle that. Also, many applications require specific isotopes of uranium, which can only be separated by very expensive and complicated techniques.