After reviewing the provided sources, I found information that might help answer your question about what caused the change in Lipitor dosage.

Lipitor, also known as atorvastatin, is a medication used to treat high cholesterol levels. The U.S. Food and Drug Administration (FDA) initially approved Lipitor in December 1996 [1]. Since then, the FDA has updated Lipitor's prescribing information a few times, which may have led to changes in the recommended dosage.

In a 2011 study published in the Archives of Internal Medicine, researchers analyzed data from over 130,000 patients and found that higher doses of Lipitor (specifically, 80 mg) were not significantly more effective in reducing the risk of heart attacks, strokes, or other cardiovascular events compared to lower doses [2]. The study also found that patients taking higher doses of Lipitor had a higher risk of developing side effects such as muscle pain and kidney damage [2].

Based on this study and other evidence, the FDA updated Lipitor's prescribing information in 2011 to recommend that the 80 mg dose be used only in patients who have not achieved their cholesterol goals on lower doses and who do not have a increased risk of muscle damage [3].

In summary, based on the available information, changes in the recommended dosage of Lipitor may have been due to studies showing that higher doses were not significantly more effective in reducing the risk of cardiovascular events and were associated with a higher risk of side effects.

Sources:
[1] <https://www.drugpatentwatch.com/p/tradename/LIPITOR>
[2] <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3016087/>
[3] <https://www.mayoclinic.org/drugs-supplements/atorvastatin-oral-route/side-effects/drg-20067003?p=1>