Thanks for providing this, I wasn’t able to find it through my own searches. I’m reading the linked documents, and can’t find anything to back up that the US courts will enforce the foreign fine. In fact, this is specifically addressed in the document and it seems to support that they will not support it.
C. The rule against recognition of foreign fines and penal judgments
The general rule in favor of recognizing foreign country judgments that meet the foundational requirements above is subject to a key exception: under both the Recognition Acts and the common law, U.S. courts generally do not recognize or enforce foreign judgments for the collection of taxes, fines, or penalties.
Given my original question was why can’t they ignore the fine, it seems the answer is that they can?