While more tech companies have been joining the S&P 500, not all of them have proven to be money makers for investors who buy index funds. Server maker Super Micro was added to the S&P 500 in March after a huge rally in the stock, driven by demand for Nvidia-based servers.

Super Micro shares peaked soon after that announcement but then tumbled in the ensuing months as the company failed to file its financials on time. The stock is about 60% off its peak, and the company said on Friday that it received an extension from Nasdaq to keep its listing.