It's so the non-EU users won't have any rights under the GDPR. All non-US users were officially being served by Facebook Ireland instead of Facebook US, which would have put them under GDPR too (like India, Australia, etc.).
I don't see it in a quick scan, but I wonder if that means all the revenue from those countries will no longer be shielded from US taxes, which might indicate how seriously FB see the GDPR as a threat.
EDIT: pdkl95 mentions in another comment, they claim it doesn't.
The discussion is here:
https://news.ycombinator.com/item?id=16872542
I don't see it in a quick scan, but I wonder if that means all the revenue from those countries will no longer be shielded from US taxes, which might indicate how seriously FB see the GDPR as a threat.
EDIT: pdkl95 mentions in another comment, they claim it doesn't.