The equity market is “skewed”

Source: Standard & Poor’s
This skewness becomes even more pronounced over the 20 years from the start of 2002 to the end of 2022. Only 6% of the companies in the S&P/ASX 300 Index beat the performance of the broader market over this time, with the top three stocks (BHP, Commonwealth Bank and Westpac) accounting for almost one-third of the total index return.

Put another way, if an active investor didn’t have those three particular stocks in their portfolio they would have missed out on a fair chunk of the market’s return.
Vanguard Australia Personal Investor