It would cost a lot more than just mapping the lines & state of the infrastructure like lanes & traffic lights in a database, which is what Waymo already does.

It would cost a lot more than just mapping the lines & state of the infrastructure like lanes & traffic lights in a database, which is what Waymo already does. Adding additional paint on the road(s) doesn't help the car know what to do when there are weird edge cases. Following lines on the road was already solved 10yrs ago and isn't really the problem.