While the cap-weighted S&P 500 is at a new high, the same cannot (yet) be said for the equal-weighted index, nor small caps. But history shows that eventually the soldiers will lead the generals, sometimes quickly and sometimes slowly.
In part , this is a matter of having to recover from a deeper drawdown, which can take time. The chart below shows drawdowns for both large caps and small caps. Small caps generally decline more than large caps, so it only makes sense that they lag in the race to new highs.