A different answer to why: They need enclosure around the goods to be transported, and right of way. You can do that by buying many expensive vehicles and nego

A different answer to why: They need enclosure around the goods to be transported, and right of way. You can do that by buying many expensive vehicles and negotiating right of way. Negotiating right of way in an densely built-up area is both difficult and expensive. Building tunnels is not extremely expensive, BTW, if you can avoid most of the factors that drive costs up. They do.