I can't comment on the bus line example, but the New York Times had a great write-up (https://www.nytimes.com/2017/12/28/nyregion/new-york-subway-...) about subway building in New York. At least in New York there's a lot more going on than the reasons you point out. Particularly damning is the fact that Paris is successfully building subways at a 10th of the cost in far less time despite having even more constraints around digging.