it's true that bitcoin is being used in many bad sectors but literally why would it stop. bitcoin is a kind of money and money can be spent/transfer anywhere in the world in exchange for some product or any service. bitcoin is also used by deep web and most probably for all kind of crimes. we can see the recent ransomewhere attack which also demanded Bitcoin from common users.
Well based on what you've said, the reason why they choose Bitcoin over Fiat is because of POWER. Having FREEDOM in using bitcoin is quite very powerful you see, I mean you can do almost anything by using it and no one will even know you did it. Anyways in Bitcoin 'everything is permitted'.