We got much more programmable GPUs over the years, but first consoles with GPUs that could conceivably run Nanite came out only in 2013. And Nanite really loves streaming of a lot of small data packages from drive, and for this SSD is really instrumental. That's why Nanite wasn't really feasible before(you don't really make fundamental AAA engine tech that runs only on PC if you are not Chris Roberts).

Nanite is basically a really complex compute shader reimplementing a rasterizer, along with generating LODs only for what is being seen, at the appropriate level, no matter the zoom (instead of fixed amounts of LODs)

So, Compute Shaders are relatively recent, anything DirectX 9 era and before is right out. Then, you still need a solid enough GPU to run that at interactive framerates, and fast storage to stream all that data in and out. And finally, there was simply no or very little research on the subject.