You could even have human pilots meet up and drive them through cities, and let the trucks drive themselves on the interstates, just like ships have maritime pilots navigating harbours.
Self driving experts can easily pull in salaries of $5M plus per year, and this stuff takes many years. To build a team of those people, you need to burn an insane amount of cash.
That much cash is only available from investors if the reward is huge. Replacing all interstate trucking is a much smaller potential reward than replacing all human transportation.
Hence everyone is working on the harder, but much higher reward projects.
I think this is an exaggeration by almost an order of magnitude, unless you are referring to the handful of people that have had successful exits in this space.
Only recently approved, though: https://www.smartrailworld.com/mind-blowing-rio-tinto-autono...
Some day some billionaire will figure out there's a bunch of wasted potential in the train transportation network and get to work fixing it.
https://www.economist.com/business/2017/09/30/rivigo-is-help...
But... Uber was planning to do exactly this ! https://www.youtube.com/watch?v=ge-4uWmuESQ
When n is at the much larger scale of trucks, efficient scheduling requires a large number of "slack" pilots to handle modest variations in demand.