I think that there are 2 basic reasons myself. First is the fact that there seem to be no "general" scientists around anymore . . . they have all been replaced by "specialists/Experts", those who learn more and more about less and less, until they learn a whole lot about nothing.
Second is that statistical analysis has replaced the scienific method way of actual physical experimentation, and worse, the "smoothing out" data until almost real data has been lost.
Where now those who comprehend the fundamentals of physics AND chemistry AND biology AND . . . . For that matter, what happened to those with knowledge of simple (or not so simple) arithmetic or algebra?
What does 400 ppm (CO2 actually mean in simple terms? It means 40 molecules of CO2 amidst 99,960 molecles of almost entirely first N2, and to a far lesser amount O2.
Since the best estimates of human caused CO2 are about 2 1/2 % of the CO2 produced, that would mean a single molecule of CO2 amidst 99,999 other molecules.
What person in their right mind would think that a single molecule of any substance could have any significant effect on 99,999 other molecules?