This is not part of what we are discussing, but why Wikipedia is referring gambling as an illegal activity? If gambling is not legalized in some countries, that does not mean that many countries do not support gambling. In fact, there are some countries that see bitcoin and other crypto to be illegal, but that does not mean cryptocurrencies are not legal. Most countries support Bitcoin and many countries are supporting gambling. Gambling is legal.
The first thing is that Wikipedia is not an authentic source of information because every person can upload their suggestion or views on Wikipedia and that does not mean that a thing that is prohibited for them would be illegal for all the persons and in every state. There is a religion where gambling is prohibited but it's only for the belivers of that religion, the rest can do it.
That is why some criminals that know about mixers are using it. But the point is that not only criminals are using mixers. Even some people that are using mixers took their bitcoin from a platform that is centralized and mix it before sending it to their wallet. Some people may prefer to use a mixer after dust attack. There are also several good reasons people are using mixers. Some people do not just take their privacy to play. Some people do not play with privacy because they see it as a way of having full freedom.
This is a mentality that shows how much they are in opposition to Bitcoin. Bitcoin mixing is a tool that some people use just to hide their identity. There are some illegal activities but that does not mean that it is spreading allowing criminal activities. The ratio of money laundering and bitcoin mixing is like 3/100 which is very rare and more activities are occurring in government affairs than this money laundering using bitcoin, but the Thing is that they want to find a route to ban bitcoin on the wish of the elite classes bankers.