Sorry, I was sloppy in saying that the judgment itself would be quashed. What I meant is that any attempt to enforce the judgment would be quashed. Since (by assumption) the defendant doesn't any assets in Europe to pay the fine, enforcing the judgment would require going after the defendant's assets located in the US. American courts will typically enforce foreign judgments from 'friendly' jurisdictions, but if the judgment is incompatible with American law, American courts will quash any attempt to enforce the judgment in the US.
Of course, Facebook and other large American corporations can be expected to comply with GDPR, since the cost of compliance is much less than the opportunity cost of being excluded from the EU market.
Sure, but these are two entirely different matters. Having an open, unenforced judgment against you might lead to complications, for example if the defendant happens to travel to the EU. It’s unlikely that a minor fine will be enforced by snatching the defendant at the airport, but it could at least legally an option.
Or the defendant may later open up a German subsidiary or plan on selling to a company with a german subsidiary. Things would get complicated in those cases.
So it’s important to be somewhat precise here - no enforcement doesn’t equal squashed judgment.
Of course, Facebook and other large American corporations can be expected to comply with GDPR, since the cost of compliance is much less than the opportunity cost of being excluded from the EU market.