If you've been in this space for a little while, you are very much aware of the big hacks. These events that scared, for lack of a better word, the confidence of investors, but without a doubt led us to where we are today. There literally thousands of BTC that have been stolen, and even though they may lay dormant for a while, eventually the hackers begin to make their moves.
You might not be aware that today these stolen coins get tagged, if you will. In other words, when they are removed from the exchanges, the wallet addresses are stored and kept in a list. When they move, everyone pretty much knows, and it would be close to impossible for them to sell it in any "traditional" way.
The Binance hack that happened just a few weeks ago is a prime example. All the funds are likely to stay in those wallets for a few years. Yes, they might use scramblers, but even those are being supervised at this very moment, and some scramblers are shutting down because of it.
If it's so difficult to use stolen funds, then.... Why do it? Well, because it's just like any other black market, where there's a will, there's a way. And, I'm sure those criminal minds with the right connections can buy these stolen funds at a hefty discount too.
Imagine a hacker being able to purchase these Bitcoins for 50% off or so, because this hacker has devised a way to "clean them", albeit in a very slow methodical way. How could you stop a P2P cash transaction meant to purchase stolen BTC? Sounds hardly possible.
That being said, unless strong regulation comes into this space, and the people who steal crypto are literally left holding unusable funds, this is likely to always happen. The never ending battle between the white hats and the black hats, good versus evil, as subjective as such notions can be.