That's a fair point that the inclusion criteria are applied consistently, not arbitrarily. But I fundamentally disagree with their inclusion criteria. It was designed for traditional companies with low growth and high GAAP profitability, not high-growth companies rapidly reinvesting into the core business.
Amazon is infamous for having positive cash-flow yet running near-zero GAAP earnings for nearly two decades, because they reinvested absolutely all profits into the business. They were famously unprofitable, by choice of Jeff Bezos, and he created one of the most successful businesses ever. Under your logic, Amazon didn't belong in the index for most of its most important growth years. Only when it became GAAP profitable, it was allowed to enter.
SpaceX is cash-flow positive in its core launch business. OpenAI and Anthropic have tens of billions in revenue. These companies have found product-market-fit, and clearly demonstrate working business models. But neither of these companies satisfy one specific accounting metric that the S&P 500 requires for inclusion, so they get shafted.
The market has already priced these companies at giga-cap levels, these are some of the largest companies ever created, and that is a clear signal of something. The benchmark index should include these companies in some form, rather than gate them behind an antiquated metric.
I don't think earnings is an antiquated metric for valuing companies though. Other metrics exist to estimate future earnings and attract a different class of investor looking for different risk/return profiles than people wanting to index companies big enough to generate steady returns with fairly high confidence they'll be doing a similar thing tomorrow. If people want to invest in a different type of company from the companies the index was designed to capture they're entitled to do so: if their expected returns are that good you don't need to browbeat indices into changing their entire ethos to get funds involved in their IPO.
Sure, some companies which vastly outspent competitors on growth became very successful profitable midcaps and joined the relevant indices when they did, but everyone else waited their turn (including the ones that never became profitable midcaps because the money tap was their moat)
You can just buy the stock, you know. Nobody is keeping it off the exchanges. Or you can buy another fund that includes it.