But no one is alleging Kotaku broke an NDA or obtained the information illegally (eg through outright theft, not via leaking), so the entirety of your point is moot.
If we assume that information regarding the development of a particular game is protected under NDAs (which is a very safe assumption to make,) then it's safe to say that
someone broke an NDA in order to leak the information.
IP law is ugly and complicated, and I know this first hand. I worked for a company that was developing a new product. Information about this product was published and it cost us a competitive advantage. There were less than 200 people on the project and they were
all under NDAs.
Someone in our company obviously broke an NDA, and the journalist who printed the story
had to have known that someone broke an NDA. (It's unreasonable to think otherwise.) We couldn't prove
who broke the NDA, however. If we could, legal action could have been taken against both the employee who broke the NDA
and the journalist who knowingly solicited the information that was protected by NDAs. Legal action wasn't possible, but it was clear to us that the journalist acted in bad faith so we cut her off. We were under no obligation to deal with people who we viewed as unethical. Make no mistake about it: It's not "good journalism" to reveal information that was obtained by unethical means.
Perhaps my personal experience are skewing my opinion on this issue. I'll take a step back here to give Kotaku the benefit of the doubt. Maybe they didn't break any NDAs and maybe they weren't aware that anyone else was breaking any NDAs by providing them with information. It's possible, right? It seems unlikely to me, but I'll admit that it's at least within the realm of possibility.
I've never been convinced that this issue was entirely about leaks in the first place. As many people have pointed out, leaks happen all the time. Gaming journalism is more-or-less built off of leaks, after all. Kotaku certainly isn't the only source to post leaked information over the years, so my initial point of contention still stands: There could be any number of reasons why Kotaku was blacklisted.