But you know what Bitcoin is good for? Paying ransoms. A very considerable share of ransomware payments is done in Bitcoin, because it solves the problem of fiat payments - they can't get frozen and have no KYC, so it's a very safe and convenient method for criminals.
Ransomware is actually a quite good argument in favour of my proposal of an "agreement" between mixers and law enforcement. If you are threatened to pay for ransomware, you can tell the authorities the transaction you made. Perhaps you can even tell a whitehat hacker group and these will contact mixers for you if the ransom attack involves a kind of extorsion you don't want law enforcement to know about.
If the criminal is trying to mix the ransom coins through a mixer which participates on this agreement, then these funds could be very easily frozen. If instead he does an atomic swap or CoinJoins the probability is high he can hide. The easier these tools become to use and the higher the anonymity degree is, the more criminals will choose these options instead of mixers.
Most bigger fishes will of course know about the mixers participating on such an agreement. But criminals are not perfect, they often are not overly competent, above all if they're script kiddies, so there are chances for some to be caught.