That's right. Using cryptocurrency is one thing, and staying anonymous while using cryptocurrency is another. The ordinary criminals may jump in to use Bitcoin or Monero. But he may not be able to convert these cryptocurrencies to fiat or other physical assets. And he may not be able to keep his cryptocurrency transactions secure (i.e without any links that can be traced back).
Unless they use mixer which is a favorite thing to them. But yeah, I agree because most criminals prefer using fiat because banks can cover for them and they can use this dirty money to buy assets that will clean their money.
If by any means criminals start adopting crypto in mass (especially privacy coins), we could expect a full government crackdown on the entire industry. Which is why I think it's best for criminals to continue using Fiat for the sake of the crypto/Blockchain industry's growth worldwide. But we'll never know what will happen in the future. Thoughts? 
They would have done it with banks if the government really has the means to fully crackdown criminal. I doubt they will have the resource and means to do it especially that cryptocurrencies are spreading and being adopted in different countries. It's inevitable to really stop criminal cases with cryptocurrencies and it will still grow because criminal sees opportunity with it. Fiat has just been around for the longest time which is why they have the most records of crime and launders.