Regardless, its amazing how simple DNNs are. People have been working on computer vision and AI for about 60 years, and then a program like this comes along which is only around 500 lines of code, conceptually simple enough to explain to anyone with a reasonable mathematical background, but can nevertheless beat humans at a reasonable range of tasks.

I get the impression it's a hardware issue. See for example http://nautil.us/issue/21/information/the-man-who-tried-to-redeem-the-world-with-logic - McCulloch & Pitts invented neural networks almost before digital computers existed* and he was working on "three-dimensional neural networks". They didn't invent backpropagation, I don't think, but even if they had, how would they have run, much less trained, the state of the art many-layer neural networks with millions of nodes and billions of connections like we're seeing these days? What those 60 years of work gets you is a lot of specialized algorithms which don't reach human-parity but at least are computable on the hardware of that day.

* depends on what exactly you consider the first digital computer and how long before the key publication you date their breakthrough.