I have no insight, but looking at the text you highlighted, I expect they must have done exactly the analysis you suggest. It is likely that the researchers an

I have no insight, but looking at the text you highlighted, I expect they must have done exactly the analysis you suggest. It is likely that the researchers and the audience want to understand how to get more effective drugs onto the market more than why placebos per se are becoming relatively more effective. This may explain the unexpected reporting emphasis.