Unlike mixers, torrent sites don't require much trust: anyone can create one and have users the next day.
And truth. But something similar can be done with mixers.
I think the problem is always related to the dimension that the mixers may have. When they become too big, they end up being more exposed. Sometimes it's better to win a little at a time than to win a lot and have big problems.
But of course this is just my perspective on things, I could be wrong.
One option for a way out of mixer owners to avoid prosecution would probably be for them to implement KYC and though it defeats the primary privacy objective, there is a logic behind it. If any form of KYC were to be implemented by a mixer then the amount of trust being given to them by their clients would be immense and basically a huge put-off.
Maybe you don't even need to go that route. They can only create a value limit per mix.
In almost all countries, there is a maximum amount that is not considered a bribe. So if this value is not exceeded in each mix, there probably won't be any big problems.
Of course, I don't know all the legal criteria that can be followed. But, the owners of these sites, have to study more the laws of the countries where they operate, to try to protect themselves.