Bell Labs was only pseudo private. The government required they have that research lab in exchange for being allowed to have a monopoly. One should also consider that institutions like that were partly so productive for being at the right place and time in history, when we were developing the tools to exploit the low hanging fruit nature has to offer us. That whole era, we snatched it all up quick. Spaceflight and such didn't stagnate after because we turned to idiots, but because mass and aerodynamic drag and Newton impose pretty inalienable constraints.