See how VIX recovered from the orange-red cross level to the red-red cross, while it took the orange-green cross of CVOL to go till the green-green cross almost double the time. If the increase would not have continued on VIX the derivative would not have had a chance to retrace to the same value even if VIX did. In other words the increase of VIX has to be quicker than the decay of the derivative.