this benchmark has to follow the market and reflect current market conditions

Sure, but right now they don't know how the market will react, so changing the index rules before there's any data would be a measure of their heuristics (e.g. what they believe the market will do), not a measure of what the market is actually doing.

The core issue is that S&P requires companies to be profitable for 12-months to get included in the index. Yet all of SpaceX, OpenAI, and Anthropic are highly unprofitable, because they are prioritizing investing all free-cash-flow into growth instead of returning money to shareholders. These companies likely will not be profitable for years, and without a rule change it's unlikely they will be included in the index anytime soon.

Given these large-cap companies currently represent ~5% of the U.S. stock market capitalization, it's difficult to justify why these companies are excluded from a large-cap index.