They shipped the Wii encryption key along with the emulator. While there's no established legal precedent that encryption keys are protected by copyright, it's largely been assumed by those in the industry that they are. It's also blatantly a measure to circumvent anti piracy measures. If Dolphin required you to go find the Wii encryption key on your own and input it into the emulator, Nintendo would have no grounds to stand on, but they screwed up and risked everything by one of the most infamously anti emulator, litigation happy corporations on earth
It's more of the usual guilty-till-innocent so it had help getting killed in the Steam crib. Overlord Nintendo wins again. You will never own what you buy so long as the big companies say you don't.
Did you read the article? This is Valve’s doing, not Nintendo. The keys weren’t even in question. Valve is requiring the Dolphin devs to get permission from Nintendo, something that will never happen.