While there is plenty of classical robotics code in our planner, I wouldn't want people to assume that we don't use neural networks for planning.
Just because we don't deploy end-to-end models (e.g., sensors to controls), but have separate perception and planning components doesn't mean there isn't ML in each part. Having the components separate means we can train and update each individually, test them individually, inject overrides as needed, and so on. On the flip side, it's true that because it's not learned end-to-end today that there might exist a vastly simpler or higher quality system.
So we do a lot of research in this area, like EMMA (https://waymo.com/research/emma/) but don't assume that our planning isn't heavily ML based. A lot of our progress in the last couple of years has been driven by increasing the amount of ML used for planning, especially for behavior prediction (e.g., https://waymo.com/research/wayformer/)
Removed that "manually" world so now it describes exactly what you would have to do to train an end to end neural network.
NNs don't get information from nothing, you would have to subject them to the exact same obstacles, geometries and behaviors you coded on the manual version.
Big edge cases have little edge cases that require their own code / and those edge cases have smaller edge cases with yet more code.
My shorthand is "the real world is a fractal of edge cases".
One good bet based on Waymo's decision to expand is that the amount of supervision each robotaxi needs keeps going down, so supervision is not tightly coupled to fleet size.
It's fuzzy and plastic and complex, but the brain has functional areas, there is intelligence more local to specific sensors, pipelines where fusion happens, governors and supervisors, specific numeric limits to certain tasks, etc.
This is a bit akin to your "listing every possible item", in a way, in the sense that there are definitely finite structures tuned toward the application of being human.
This interplay via our supposed "AGI" and what is "cached" in our also not static but evolving hardware is really one of the most fascinating aspects of biology.