Probably because the title of the article uses 402,000,000 Mbps and I think there’s a rule(?) on HN about not misrepresenting titles or rewording them too much, though I’d wager 402 Tbps is fair alteration.
It’s like those USB battery packs that advertise “20k mAh”. They clearly do not understand SI prefixes.
I'd wager it's the average person not understanding and the marketing team just appealing to them to make it less confusing, kind of like that third pounder story.
It’s like how we still specify power plants in ‘thousands of megawatts’ instead of gigawatts, I assume because of the back to the future reference