What's with the price-dependent periods of reduced volatility?

I was reading a [reddit post ](https://www.reddit.com/r/wallstreetbets/comments/1katbrx/visualizing_the_last_10_years_of_spy_daily/)where the author shared this analysis. The author posed a question about selling calls, and - to my surprise - nobody talked about the periodic repetition shown in the column. I've been thinking on it, and I can't think of a good reason why there are these nearly-periodic contractions of volatility at price points. (magenta curves on the drawing) They exist at the same levels which we find the greatest price movements (green squares on the drawing) but I can't determine if there's a connection between those. Looking to anyone who may have some insight -- why are there volatility contractions dependent upon the price of SPY?