in theory, people that do this for a living know this? shouldn't they all be raising the red flags on this, as opposed to say just people on hackernews?
No, because the indices are free-float weighted not cap weighted. The float planned for SpaceX is tiny. If it were purchased by the indices at 1.7T on Monday and went to zero on Tuesday, the amount of value lost by the funds would be barely larger than the normal daily fluctuation of the market.