The S&P 500 has been hitting highs in a rally that's had only modest sell-offs.
Here is a chart from BusinessInsider illustating Societe Generale's Andrew Lapthorne's research.
Lapthorne notes: "The number of 1% down days for the S&P 500 in any given year has averaged 27 since 1969; the S&P 500 has seen just 16 1% down days over the last 12 months. It has now been [almost 500] days since a market correction of 10% or more, the fourth longest period on record, and, as we show below, the annualized peak to trough loss has only been 5% compared to typical annual draw-down of 15%."
As you can see, recently, volatility has been dramatically below normal.