They can track it just fine. It goes straight to North Korea.

How do/did they get it out though?

russia? others who dont care all that much?

the laundering wouldnt be all that hard to take those buttcoins on in exchange for clean ones.

business laundromats

useful idiots in the US who buy crypto because "it's the future"

These idiots can't.

Because all the exchanges they'd use are regulated in some form and at least adhere to anti-moneylaundering-directives and boycotts, or they can't operate in the US and/or EU.

Sure, they could move to p2p exchanges or exchanges in unregulated jurisdictions, but that requires quite some effort and thought. Which, by definition, would exclude them from being "idiots".