A lot of their revenue is also investment from hardware and software vendors that are using the revenue from the AI companies for those investments.
It's like the Enron scheme, but instead of one company inventing fake companies to move money around to increase revenue and drive up prices to hide the fact they're hemorrhaging money while the C-suite tries to divest their own money from the company, it's multiple companies working together to move money around to increase revenue and drive up prices to hide the fact they're hemorrhaging money while the major investors try to find a way to cash out.
Anthropic is anxious to do their IPO because they know their business model is fucked, and their shareholders want out.