Why does it have to be government R&D?

It doesn't, but it was, because it was tied to administration and nuclear physics and then rocketry.

Private sector doesn't do much without obvious short-term gain, and it especially doesn't do basic research. It may be good at fitting more pixels in ever thinner phones, but it wouldn't get to that point if not the government that needed number-crunching machines for better modelling of nuclear fission some 80 years earlier.