The market cap of the S&P 500 according to Google is ~$65T. Anthropic, OpenAI and SpaceX could well amount to $4T+ in market cap. That's ~6% of the entire index. It's like adding another NVidia. That's a big deal.
The rules around index inclusion exist for a reason. Too much control in one person's hands (which SpaceX has), too small a float (so you don't get price discovery), lack of a history of financial performance and minimal trading days just don't give investors confidence and, like it or not, investment decisions are made based on the index. If you want to argue against passive investment, well, good luck with that.
I think a lot of people have this weird idea that what we need is some theoretically unfettered market for "true" price discovery when it's actually regulations like this that create markets. It's like a libertarian brain worm.
I don't think anybody wants these mega-companies out of the index, specifically. They just don't see why rules that exist for a reason should be suspended when the net effect of that is that investors have less information and there is a lot of forced purchasing. If you have confidence in your IPO, let the market decide what it's worth without trying to fix the price because what they seem to want is for insider lock-ups to end about the time we'd otherwise be getting normal price discovery. Kinda weird.
Investor confidence needfs to be managed by creating a stable, regulated market.