Actually, crypto is not too difficult to track. Blockchain analytic companies like Chainalysis, Elliptic etc, have shown that cryptocurrency can be easily traced. However, I think the reason criminals prefer crypto in carrying out nefarious activities is because it has greater anonymity. Traditional banking makes use of bank accounts tied to users identity, and as such, they can be easily identified, while crypto does not. It makes use of wallet addresses that are not tied to their identity. Another reason is that crypto is accessible and cannot be frozen (except those issued by centralized entities and the ones on CEXs).