Public funding has an exponential effect on the number of articles produced and the number of subsequent citations. The bigger the investment, the more students are paid to do the research and the more often large research groups are created, which results in further developments or a broader network. The more people involved, the significantly greater probability of citations. The curve goes down because there is not enough money to pay students. But then the increase you see is more or less exponential. There is a negative spiral when there is not enough money to pay enough students or fund enough research, but then there is a snowball effect when the research is funded.
What I mean, in a nutshell, is that you have to have a minimum amount of money if you want to produce enough quality research.