Because the people who are writing about it are getting it partially wrong. They still need a federal warrant. And to get that they must show enough proof to be able to say your a suspect.
Generally speaking, sanctions are a still major deal. All your US and international bank accounts (the ones they can find) are frozen.
They can have you locked away from the general public without a phone call for months...not hours or days but months. It can even become years if they find enough evidence against you. It's like they make you disappear without a trace, only worse. Of course this is the worst case scenario. Don't be an idiot and intend to harm and/or steal money from other parties and your safe.