Fiat money is easy to get and more reliable to accessible. You can easily steal fiat than cryptocurrencies.
Blockchain innovation makes their security more intense to break and criminals would prefer not to waste their time by hacking it.
But if the criminals are smart like a scammer ( who may consider as a criminal ) it can easily misdirect people and stealing their coins.
Indeed, when we talk about criminals attacking banks or robbing money, even trading illegal items, they often do not trust each other between transactions and they always prefer the speed of transactions, cash is always more stimulating, not too many criminals like to waste minutes or even hours getting a transaction confirmation, more than enough time for the police to arrest them. But maybe in the future, criminals may be smarter, apply crypto to optimize anonymity, the government will be more difficult to find but there is no doubt that crypto regulation will become more closed