Liquidating the privacy coins into fiat cash is one of the biggest barrier to them because they can't stay completely anonymous while using internet at some point they will leave their traces which could be never erasable.And also not much of those criminals doesn't know the existence of cryptos that is why they prefer hard cash over banking transactions.
I agree. This criminals will just preferred fiat/physical currency because its easy for them to use it, without any private keys and KYC to consider.Unlike Cryptocurrency, the can be trace as few mentioned here. I think, they will absolutely have a hard time on crypto and will be caught easily through their trace upon accessing the internet. Maybe a few could do well, especially if the criminals is an expert, but i doubt if he'll have a successful tansaction over the advance technology.