Why are hollow conductors used for signals of a certain frequency?

So this question is really about skin depth. I have been introduced to the skin depth by a simple model (simple equation for electrons in a metal with a damping term) of polarisability for a metal. In this calculation, using the dilute form of the classes most relation the permittivity of the metal was found. This had a complex form, and thus so did the refractive index.

As a result the wave vector of any electromagnetic signal is complex and the complex part attenuates the wave and represents energy loss. I understand this part. However, I was then told that this is the reason that sometimes hollow conductors are preferred (like a hollow copper tube). Because beyond the skin depth the field is rapidly attenuated. However, surely the attenuation only takes place in the direction of the wave vector k? How would a hollow tube cary a signal? If the k vector is along its long axis? Surely it gets attenuated by the time it reaches the end?