You still misread the article: they observe the nearly constant 2% growth across the long timespan, regardless of the relative increases in researchers, regardless of all the policy changes, regardless of ...

The article is NOT about some recent change. Please cite the article if you believe it is trying to solve a puzzle concerning a recent change.

The whole point is that this 2% seems to be robust, regardless of investing or getting more ideas, invalidating the idea that the growth is a simple result of the production of ideas (say making blueprints for a new kind of factory, which can then be copied without having to make more blueprints).