So much money has been invested in Anthropic and OpenAI at this point that to declare it a loss and walk away could potentially destroy a lot of VC firms, and a non-trivial chunk of the US Economy.
Good luck hiding your huge sunk cost of bilions and billions in there bro. I wish people who had zero understanding of actual finance would never comment about it.
Moreover if they declare their existing assets are bunk, the valuation is marked down, especially after now pricing in failure risk - this is catastrophic for VC's.