If you want to imprison all the murderers, you can accomplish that goal by imprisoning everyone but we don't do this and most people would recognize that the idea is mad.
So the test here for any regulating authority should be, is your regulation harming the innocent in some way? If so, the imperative is on you to find a better way to go after the guilty, if you don't you have become an enemy of the public good and your moral authority is lost. We can get into specific regulations but I think with modern KYC and AML we are absolutely at the point where they contribute to the suppression of economic growth and individual liberties and need to be dialed back.
The point being, sometimes undercutting criminal activity can be done be legalizing the activity rather than introducing more types of illegal activities to try and detect the original ones. The cure is sometimes worse than the disease.
The $10k rule by the Bank Secrecy Act wasn't indexed to inflation and would be closer to $80k today. So it should be amounts up to $80k that aren't considered worth monitoring, but instead, if you deal with, say, buying and selling cars, you get tripped up by that all the time. It's regulatory red tape overhead that costs a legitimate business extra time money that they could be better spent elsewhere.
And even you yourself answer the main question - it doesn't stop criminals. Just makes it more expensive.
why is it a bad thing to make criminals expend more effort and money?