The diameter of the resulting tunnels is too small. They are not as large as subway tunnels. Also, many tunnels used for public transportation are built as cut

The diameter of the resulting tunnels is too small. They are not as large as subway tunnels. Also, many tunnels used for public transportation are built as cut and cover rather than bored tunnels. It's much cheaper. E.g., most of the New York Subway. There is no room for rapid disruption in the technology because it's been around so long. This is just like how you don't see many startup companies coming in and deciding to disrupt the hand tool industry or the I agree about getting back to the point of contention: what I was really saying is that Twitter and social media sites like it are a well-established business model. Twitter isn't losing money for Elon because Twitter was a company with bad fundamentals before he bought it. Twitter is losing money for Elon because he overpaid for the company and has mismanaged it compared to his predecessors. If Twitter were a public company today it would have more users, higher market cap, better customer satisfaction, and either higher profits or more modest losses. Twitter may not have been spectacularly profitable but it was in no way shape or form endangered or mismanaged before Elon took the helm.