Simply, the controls. For a criminal, the first problem that arises when he has a large sum is how keep it. However, if he went to the bank to deposit this sum, the banker would be forced (normally) to ask where those funds came from. This is why the criminal uses cash, because instead of depositing it in the bank, he can go (for example) to a jewelry store and buy, in cash, a Rolex which still remains a luxury item that maintains its price over time. This obviously for the common criminal, certainly not for Tony Montana
