Personal opinion below. I work for DFINITY, but I do not have any authority to speak for them.
As I understand it, copyright holders need to consistently enforce their copyright if they want to enforce it at all. I.e. if Nintendo were to turn a blind eye to a canister hosting a game they own the copyright of, anyone in the future could point to that as proof that the copyright is not being enforced and be legally allowed to do the same.
I’m not a US citizen and not particularly familiar with US laws regarding copyright enforcement (such as the DMCA), but my understanding is that if a node operator does not respond to a takedown notice, the copyright owner can simply escalate to the data center (note that node providers are not actual data centers, just a couple of racks of servers in someone else’s datacenter) and ask them to essentially unplug said servers.
Meaning that if the NNS (or whatever judiciary is put in place alongside the NNS acting as legislature) decided to ignore a takedown notice, this would likely result in all nodes in the US getting unplugged one rack at a time over a period of a few weeks. Possibly in other US friendly countries too. All this with no need for costly legal action on the part of the copyright holder, but merely sending a handful of DMCA notices.
The canister controller taking down the respective canisters themselves is of course the ideal outcome, but this cannot be the expected outcome except in a very small number of cases. Meaning that we, as a community need to put something in place to deal with this type of issues all the while weighing.the possible consequences against the benefits.
I can sympathize with both sides of the argument (taking down illegal content; and censorship protection) and I definitely don’t have a solution for more gnarly cases (e.g., to pick a random example, marginal holocaust denial), but my personal opinion is that a clear cut copyright case is not worth the consequences. I am oftentimes the person who likes to see (a small corner of) the world burn, but in this particular case, I believe it would be exceedingly anticlimactic.
(To address one comment above: no, DFINITY doesn’t know the identity of canister controllers. And it also didn’t in this case. Someone somewhere (e.g. the exchange that sold them the ICP) might, but DFINITY is not privy to that information. In (not so) extreme cases, the canister controller might even come in the possession of ICP/cycles without ever having to divulge their identity to anyone. e.g. by getting an NFT drop and selling it.)