Targeting mixers (who don't even touch fiat money) is even more problematic for governments. An honest mixer can easily recover from authorities shutting down clearnet domains or seizing servers. New infrastructure can be built within days and proper encryption would protect all customer funds in the meantime.
But the Bestmixer case -- and subsequent disappearance of BitBlender -- highlights the biggest problem for us: Law enforcement temporarily shutting down a mixer creates an opportunity for them to exit scam.
I am almost positive Ciphertrace's technology can still trace movements of transactions even after they've gone through a mixer
That's possible to an extent,
particularly mixers that are using outdated and broken algorithms. However, if companies like Ciphertrace could conclusively break all mixers, governments would simply surveil mixers
rather than trying to shut them down.
Either way, this is irrelevant to the larger point, which is:
Governments can't shut down mixers. They can only shut down domains and seize servers. These are small, temporary setbacks.
Of course, nobody was arrested in the Bestmixer case. They just disappeared with everyone's money. Same with Bitblender. These were exit scams.