The coriolis term in the equation of motion for a rotating coordinate system is proportional to velocity.
The convention is to define a potential when at each point in space the force exterted (for instance gravitational force) is a function of the position coordinate.
As we know: the potential difference between point A and point B is the negative of the work done in moving a test mass from point A to point B.
That is what allows the concept of centrifugal potential to be defined.
In the case of the coriolis term:
As we know: the coriolis term vector is perpendicular to the instantaneous velocity.
The definition of work done is displacement in the direction parallel to the force exerted.
That is: if a force is always acting perpendicular to the instantaneous velocity vector then the effect of that force does not fall in the category of work done.
As we know: the coriolis term vector is perpendicular to the instantaneous velocity.