Cryptocurrencies can be mixed. If you engage in very basic precautions, such as doing something easy like transferring your money to monero, and then back again, it is effectively impossible to track where your money came from.
Once you get to the coffee shop stage, nobody knows where that money came from.
With today statistical analysis methods is trivial to track big flows through various block chains, even if some of them are totally hidden. And they only get better by the day, with your traces sitting there like a duck.
And you don't need to be 100% certain, it's enough to get a pool of suspects which then you can analyze/surveil with other methods.
You still need to get on at some point. Plenty of people are willing to wait a few hours to get confirmed so the price never hits zero. Further, even if it did work you would make your mixing transactions stand out more while also vastly lowering the number of them.
Once you get to the coffee shop stage, nobody knows where that money came from.