Bitcoin mixers and coin mixers in general are only designed for criminals and are only used for criminals.
I think most criminals will prefer privacy coins like XMR rather than going in the hassle of bitcoin mixing service. But again the service of bitcoin mixer is not made to use it negatively. Its just that most people use it for illegal purpose and not for the good cause.
Cyber criminals still use bitcoin, because its still the most used currency in the darknet (for whatever reason) and the most easy to use coin for ransomware (most known and easiest to get for ransomware victims). New ones started using XMR and its getting started more popular in the underworld. XMR would be worth an additional post
