The linked article obviously has a gold-bug agenda. That's why I think it's important to bring one more argument in favor of the root cause being some physical constraint, rather than legal or organizational:

At around the same time, the growth of GDP and standard of living dramatically slowed down in the Soviet Union, too. From venerable ~5% per year in 50s and 60s, to ~2% in 70s, to ~1.25% in 80s.

Different legal, political, financial and managerial framework, the same decline.