That's why you use mixers. Good mixers will completely break the chain between inputs and outputs.
Why are mixers legal? The only purpose I find on them is to money launder. They are literally useless if you don't have anything to hide.
I was thinking as you mate, why mixers still legal?
The exchanges have to send the bitcoin back if they come from a hack but why no one says the same for Mixers? Those are money laundering machines and no gov is interested in stopping them.
Maybe governments are ignorant and they don't know a tool like this exists. That's why they are not getting banned yet. But they will not live forever.