Apart from pointing at Asian nations building subways in almost every big city, it might also worth a look to the Arab Peninsula, with also very high speed of digging and building required infrastructure. It is only US who is behind at this sadly.
This is a problem in Europe as well. The new North south line in Amsterdam cost over 3 Billion to complete and took well over a decade to build.
China is indeed digging at huge speed.
My understanding with the Boring company is not that they are doing anything particularly special but merely doing things in a way that facilitates economies of scale. So, they standardize designs, equipment, logistics, etc. and they use automation. If you do a one off tunnel with a machine that will only be used for that tunnel, that doesn't make sense. If you are planning to do many tunnels that makes a lot of sense.
