Vol at the index level is a joint function of the vol of the stocks in the index and the correlation among them. It's the incredibly low level of the latter that has been Ozempic for index volatility. "Low correlation each day keeps index vol at bay" Here's a chart that shows it. Assume 35 for the vol of the average stock in the $SPX. With the $VIXEQ at 38, that's a reasonable assumption. Now choose different correlation levels (horizontal) to yield different index vol outcomes (vertical). Actual 3m realized correlation of the stocks in the SPX is (wait for it) 3%. One year is 7.5%. Let's move correl from 7.5% up to 30%. SPX vol essentially doubles, up from roughly 10 to 20. And that assumes no change in average single stock vol. We know, empirically, that stocks become more volatile and more correlated at the same time. A joint shock higher to both will seriously boost realized vol at the index level and take the $VIX much higher in the process.