By no means am I an expert in the field of crypto or economics. And I'm sure the subject matters here are incredibly more complicated than perhaps this oversimplification. But from what I understand, the whole purpose of crypto is to have a decentralised currency that can be freely traded anonymously. Accessible to all, controlled by no one and independent of any one group or government.

By imposing sanctions, yes, you may stop mainstream currency from being sent around the world. But depositing large sums of money into decentralised systems means that it's quite easy to bypass these restrictions. So sanctions can only really be seen as publicly announced shunning.

So there needs to be some other form of economic policy in place to prevent the transfer of wealth as the traditional objectives and methods are outdated and easy to get around.