Because the last time it was litigated in the US, the good guys won. But SCEA v. Bleem was over 20 years ago, and there's no guarantee that the courts won't roll back protections for emulation development.

NoA is notoriously vindictive & litigious, and they have more money than the Dolphin devs. Even though Sony lost the case, the lawsuit ruined Bleem. It's not outside the realm of possibility that Nintendo will try to do the same thing to Dolphin, Ryujinx, Yuzu, etc.