Given that the decision is unanimous just maybe it is in alignment with the constitution. If Clarence Thomas and Ketanji Jackson agree on something, that's some kind of signal.
For most of US history people's access to information was controlled by a few powerful news/media corporations and the Supreme Court did nothing to stop that. It's no surprise that when we finally get a decentralised information transmission system not beholden to the elites, the Supreme Court doesn't want to lend it a hand.
When the mind-reading algorithm provides each user with their own reality to live in, then we are talking about editorializing. And allowing a communist, anti-Western government direct control over that power does not seem reasonable.
inb4 "better than my own government" - great, we agree that social media algorithms are a net negative to all society.
Communications is great. Video is great. Social media algorithms controlled by rage-inducing profit seekers and governments is not great.