This is all blah.
Noah is perpetually, painfully online. He has to be, because he makes his living (a) pointing out when people are wrong on the internet and (b) trying to convince people that he's really smart. All of his interactions with reality are through that lens. Seriously, It's January 1. Go look at how many tweets and retweets the guy has on twitter in the last 24 hours.
The internet does not want to be fragmented, because the internet seeks status.
People on the internet will seek status (see: Smith, Noah), and barring that, will seek the knowledge of those who have claimed status. And as long as those with the MOST clout congregate on a single platform, the rest of the people on the internet will follow. It makes logical sense for all of the actually important journalists to centralize around a hub like twitter because it's a way for them to keep their ear to the pavement. They are expected to report quickly on issues and it gives them the ability to stay up to date on quickly changing issues. Even for things as mundane as sports, almost all sports journalism is broken first or simultaneously on twitter. Twitter is the tool. The true value is in who is using it. It's what Musk has gotten hilariously backwards and why it will eventually bite him in the ass.
The right-wing sphere has Gab, Parler, AND Truth Social. Nobody reads them. Donald Trump's own posts on his own platform get far more reach by second-hand screenshots on twitter than on the platform he owns. Candace Owens doesn't gain any visibility by fighting with a nazi on Gab. She can get a lot of views by nitpicking a post from Maggie Haberman though.
The internet has ALWAYS wanted to gravitate to central locations. The post-Usenet years were an abberation because it was a time when a centralized source for information and conversation was disrupted. Those people sought out Digg, and then reddit. They're still on reddit. If it wanted to fragment, it'd have done it already.