Why nature is ahead.
Well volume wise it helps if you can do *true* 3d packaging.
The best I'm aware of in this line was a Hughes project for some kind of missile guidance system (SDI?) stacking bare *wafers* on top of each other with feed through connectors made by putting drops of Tin on the surface and using a temperature gradient to "Drive in" the Tin to create a high conductivity path front to back. top layer sensors (vision?) then multiple layers of processing and memory.
Today a thing called "SMART Cut" uses H ion implantation to create a weak layer <10 micrometres below the surface. Build the circuit on a regular thickness wafer, slice off the top and repeat. Thickness reduction of x30 roughly, putting very substantial power into a standard chip package. If you can get the heat out.
However this still leaves you *fundamentally* in a 2d world. Neurons are simply *not* restricted in this way. They also allow fan outs of up to 10000 other neurons, while conventional transistor gates hit about 10 by design.
Power wise the brains asynchronous architecture saves a *lot* of power and eliminates the whole clock distribution problem. Today *half* of all CPU transistors are dedicated to either transmitting the clock or restoring its rise/fall times or re-synching the local clock with the chip wide clock due to clock skew.
To *really* get to human brain power levels they would have to go with Carver Mead's CalTech group using custom logic elements (but built on conventional foundary processes) as *analog* components of simulation. They've gone rather quiet lately but part of what they found was the design has to *incorporate* noise, not fight it (digital logic aims to swamp noise).
They also found that "Computation" flowed in waves across their arrays of devices.
BTW the Torus is a good architecture for super computers as a message passed even the long way round gets to its target *whatever* x,y direction it's sent in.
An interesting point about this project will be if the processors will be black box neurons and its the connections and initial data values that will be settable *only* (IE like a *real* brain) or if they will tinker with the simulator code on the nodes once built. IRL that would be more akin to supplying drugs or replacement cells through in vitro grown stem cells.
It's an interesting project and I'm not sure how much work has been done on the bridging stages between actual neaurobiochemistry and the big picture stuff. Thumbs up.