What this shows is that everyone is piling into fewer and fewer stocks in each index. i.e. FAANGM in NAS. This is pretty common when there's growing fear in the markets, and people chase momentum stocks because growth and value are declining. We can see proof of this with the Russel 2000 going sideways all year and then falling out of range. Plus US500 has a steeper decline than US100. With rate hikes coming, smaller companies will have the most problems servicing their debt and getting new loans.
If you look back there was a similar trend in 2018 that ended in a sell-off with V shape recovery.