I think part of the decline in biology specifically may be the rapid growth of NIH funded research in the 90's due to the success of molecular biology and the necessity of many warm bodies at the bench, which was followed by the NIH budget "crunch" of the last decade. This combination dramatically increased the competitive nature of getting grants and high-impact papers. In this environment, those who are careful in their claims are selected out of the career pool (not all obviously, but enough to affect the proportion).

A couple of my experiences: I had one paper in a mid-range journal where we found a very interesting biological pattern in the data, which we discussed but ultimately decided to dismiss because there were confounding factors. A very well known lab took the exact same data, did a couple minor experiments to justify dismissing our concerns, and published in a top-tier journal.

In another case, I reviewed a paper from a VERY famous lab and their own metrics proved that 95% of the data was noise. They simply removed the offending metrics and published in a different, equally high-profile journal.