> But at a fundamental level, the S&P500 index exists to track the market
No, it exists to track a subset of the market based on specific criteria and weights. It's not even based on the market cap of included companies directly.
'S&P Total Market Index' exists to track the market.
> qualify as major members of the index
Not based on the inclusion criteria.
AND even if that were changed they wouldn't be near the top anyway, despite the trillion dollar valuations initially they wouldn't even be in the top 20 by weight.
> and defeats the purpose of the index entirely.
The index has operated based on specific rules defining inclusion criteria for a while. Can we just conclude that it did not become the most popular index despite never being designed to track the full market or be based directly on total market caps.
After all it's the people advocating the inclusion of these companies are advocating an arbitrary modification to the rules just to get them in.
The "total market index" point has been addressed twice now. Nobody ever claimed the S&P 500 tracks all equities. Only you keep bringing it up.
On your claim that these companies "wouldn't be in the top 20 by weight": as I addressed to you other times in this thread, SpaceX float 1 year after IPO would be 50%, giving it an index weight of $800 billion. That places it easily in the top 20 large-cap U.S. companies. The article linked has a chart of forecast free float. Your claim is false.
https://www.economist.com/finance-and-economics/2026/06/01/c...
On "arbitrary modification" of rules: every criterion in the index was itself added or revised at some point. The profitability requirement, the float threshold, the dual-class share exclusion then reinclusion. All these rules were modified. If all rule changes are "arbitrary," so are the existing rules. The only meaningful standard for evaluating a rule change is whether it better serves the index's stated purpose.
The stated purpose of the S&P500 is to be the "best single gauge of U.S. large-cap equities." A company with a $1.75T market cap that ranks in the top 5 by size in the US is, by definition, large-cap. Excluding such a large company is contrary to the stated purpose of the index.