Analysis of transmission lines and waveguides
Generally we use the simplest model we can, that produces useful results.

A two conductor waveguide like co-ax that's supporting a TEM (Tranverse Electric Magnetic) Mode can be analysed in terms of a tranverse voltage across the dielectric (just like capacitors have) and a longitudinal current (just like inductors have) in the wires. When we measure the speed of propagation and impedance, we find they're consistent with ascribing sensible 'per unit length' figures for capacitance and inductance.

In a hollow tube waveguide, the TEM mode does not exist, and the modes that do propagate (TE and TM modes) do not map onto nice two-terminal components.

We can also analyse a two conductor waveguide in terms of fields. It's just that it's harder work than circuit theory when we're dealing with the TEM mode. When we apply too high a frequency to coaxial cable and it 'modes', starts supporting tube-type waveguide modes like TE10, then we need the field approach.