I see there are legs available with First Class upgrades available when I search with "MVP Gold guest", but the First Class fare is still more expensive than Coach. Is there price variability in applying a GGU? Or am I meant to book Coach and apply a GGU after the fact?

On a related note, why are there First Class upgrade rates for flights that don't have upgrade space available? Why even show the alert/why would someone still move forward with this purchase?