I think that one of the biggest disadvantage of bitcoin is that, it can be use on llegal transactions like selling or buying smuggle goods or even illegal trading on black market. It can also be use on illegal laundering. The transaction are very secure and private, that is why it is prone the illegal activities.
I think criminals use cash. They can also use monero, zcah and dash. I think bitcoin they no longer use, because it is not anonymous.