Today we have a tiny fraction (like 2%?) of the global supply needed to make enough robots to replace all humans.
This is before we get to the other logistics like power and the rest of the materials, but we have a path to scale those up (except maybe Copper, that's another tough one.) Turns out rare earth elements are actually very abundant, but extremely hard to mine, very toxic to extract (which is partially why China has a strangehold on those) and we don't have a good path to scale those up.
All of this could be moot if we figure out alternative technologies for equally capable motors that could be manufactured at scale, but AFAIK whatever promising is on the horizon would still take a very long time to ramp up.
First, you make a robot that mines rare earth metals. Then construction robots. Then an automated factory for assembling robots. The whole premise is that the robots are faster at these tasks than humans would be.
If the robotics are feasible their rise should be exponential, not linear, since each robot built makes building the next faster and helps to remove whatever bottleneck you had.
You can't just have a robot start mining/processing rare earths, anywhere in the country. You need permits, and a lot of money. I guess that didn't stop AI companies ... but there isn't an "infinite" novelty/hype premium for rare-earths, like there is for LLMs.
That totally does not follow. Robots can be feasible and their payback curve can still be linear or sublinear.
Take mining rare earth metals, for instance. The problem with mining rare earths isn't that it takes so much human labor. The problem is doing it without poisoning the surrounding 30 square miles. Replacing the driver of the earth mover with a robot doesn't fix the chemistry at all, nor (I suspect) does it significantly affect the economics.
To the end of it? Maybe 40?