Some version of this has been echoed over the years from fans, and it has always completely missed the point. The UFC doesn't "allow" this inactivity. The champions aren't dictating to the UFC. The UFC actually wants their highest earners to be relatively inactive. This is the UFC's business model: put one title fight at the top of the card, and stack the rest with cheap labor. It keeps overhead down and maximizes profit.
We constantly hear from fighters who are frustrated because the UFC has them on ice. There's a reason.
In theory, I agree that the UFC shouldn't placate money-fight seekers, religious holiday holdouts, rank-squatters, etc. But these things don't actually hinder the UFC's schedule.