They could arguably have ignored the decision. If a German court rules that something should not be available in Germany, they should order German ISPs to block it. That's what the UK does about "illegal" torrenting and streaming. And that's what China does about the Dali Lama, Falun Gong, Uighur resistance, and so on.
Edit: OK, so some argue that Project Gutenberg, which does business from the US, and which has no physical presence in Germany, should have done what the German court ordered. But consider the implications. Firms hosting content from a particular country would be subject to court orders from every country. That would not end well.
> But consider the implications. Firms hosting content from a particular country would be subject to court orders from every country. That would not end well.
They already are if they target users in a given country. Lack of international enforcement just means that they might escape enforcement. See also GDPR, the US case against Mega, a company run by a NZ resident and incorporated in Hongkong IIRC. See also how Twitter blocks certain tweets in certain countries lest they’re blocked completely. Same holds true for Facebook. Google censors certain autocomplete and searches in some countries. They also adhere to the EU “right to be forgotten” regulations - despite being an US company.
Sure, many companies comply "in certain countries lest they’re blocked completely". But Alexandra Elbakyan has ignored judgments in US courts against her. Under Russian law, I believe that her site is legal under fair use. She has managed to piss off the Putin administration, but that's a separate issue (as I understand it, her communist purity vs his vanity). And Google basically left China over censorship demands.
In the Mega case, the US basically leveraged their Five Eyes relationship with New Zealand to have Kim Dotcom's estate semi-illegally raided in January 2012. I say semi-illegally because it was done under agreements that are normally used against terrorists. I doubt that China could get away with rendition from US soil. No more than the US could get away with rendition of Snowden from Russian soil.
So basically, which countries get to enforce their law in other countries depends on relationships and dependencies, relative military power, and support from powerful allies. Under those standards, Germany might have a chance of prevailing against Project Gutenberg in the US. Except that the US doesn't like to be pushed around.
Ignoring an unfavorable ruling because it can't be enforced is not equal to not being subject to the laws. Alexandra Elbakyan might have major trouble traveling to the US.
Edit: OK, so some argue that Project Gutenberg, which does business from the US, and which has no physical presence in Germany, should have done what the German court ordered. But consider the implications. Firms hosting content from a particular country would be subject to court orders from every country. That would not end well.