The American DMCA defined the global rulebook for safe harbor. Europe, Canada, and Oceania have rough parity with the DMCA.
Except that in the US, you have to register an agent with the government. Outside the US a site just needs to post contact info on its web site. Inside the US a site needs to print out a form, fill it in, send it by mail with a check, and then repeat the entire procedure every time the contact info changes or the same company add a site. The check is about $100.
That’s a lot of friction! No surprise that few American sites bother to comply.
It seems like a fine point, but there is a big impact. Far fewer American sites are in safe harbor. Sites outside the US are far more likely to be within the law.
The boolean logic of safe harbor is one giant AND statement. (AIUI/IANAL). If every little detail is correct, you are in. If not, you are out. There’s no semi-in for sites that do everything right except register an agent.
So if you’re a copyright troll the lesson is clear: sue American.