Because they're expensive and unreliable for most applications. They need more power, they increase draft, they don't tolerate debris, and they really dislike rough seas.
They do fine for passenger traffic. Draft, debris and rough seas are not a problem. You need gas turbines or very unusual diesels for the power, that is the problem.
Mandate that the home/landing page of social media sites is a chronological display of people/artists/whatevers you've legitimately chosen to follow rather than maximization algorithm force feeding. For all users. The have to click to get to the algorithm zone. Problem solved.
I don't think that's really solved. Facebook had lots of engagement pre-feed. Reddit has lots of engagement even without personalisation. It's still going to be problematic for lots of people.
That's underselling the product, a swarm of nanobots that are (literally, currently) beyond human understanding that are also the only way to construct certain materials and systems.
Inheritor of the Gray Goo apocalypse that covered the planet, this kind constructs an enormous mobile mega-fortress with a literal hive-mind, scouring the environment for raw materials and fending off hacking attempts by other nanobots. They even simulate other hive-minds to gain an advantage.
