I make these kinds of maps for a living.
Yes, it's expensive, however, as we refine algorithms, and the processing systems, it gets cheaper, especially amortized over more cars, where the per-car cost becomes affordable.
ML doesn't work well enough for offline maps generation either, and all the high quality maps require human editors for final touch.
All this work is currently done because realtime perception doesn't work well enough, and you can have a much more reliable system with the aid of the maps. Having a 3D base map of the world makes the realtime perception problem far simpler, and it makes fancy sensors less critical.
In the US, where the cost of labor is very expensive, self driving will make sense, even if it's expensive, but someplace like China or India, where a middle class person can afford a driver, it probably makes less sense, though the push for it in China is probably the strongest that I've seen anywhere in the world.