>BTC does have to be turned into fiat. But I can only assume, based on how rarely people who conduct ransomware scams and the like seem to get caught, that bitcoin laundering is a solved problem.
Furthermore, professional black hats tend to have business expenses that can be paid in bitcoin so they don't even need to convert all of it.
You can't just pay your amazon bill with it; that creates a paper trail. The feds could subpoena Amazon to find you. You can only pay other dark web denizens, and only if you trust them not to use it for something subpoena-able.
Furthermore, professional black hats tend to have business expenses that can be paid in bitcoin so they don't even need to convert all of it.