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?
Well, just because of misused of those bitcoin mixers. The purpose should only for the privacy to avoid of being hacked and not for money laudering.
Example, --if you have a huge of bitcoin and you want to send it to your main wallet. You need to use bitcoin mixer just to hide where it goes and hacker will not be able to trace where your bitcoin sent and it should not be linked to your identity upon using costudial wallet that has your full personal information. But unfortunately, bitcoin mixers are used for fraudulent and the home to exit scammers of what they hack not to able to trace.