Interesting that VIX has been at an all time low for the last year or more. So volatility has been at an all time low. These last few days have been rough, though.
In general, it's usefulness as an indicator of volatility has decreased lately.
Another explanation is that VIX is being actively dampened by the growing popularity of the 'short volatility' trade. E.g., the SVXY ETF among others. We're seeing today just how volatile volatility can be!