Your answer is a simple one.. Too many people realized spending 1.4b silver will rapport them to 200 in 3 towns (perfect for a single run) and were recieving anywhere from 2-6 scrolls every 2 days. Therotically that seems amazing to us but in PA reality that is months and months ahead of where the average mercher should be at. Therefore a nerf in "drop rates" was needed in Pearl Abyss' eyes to slow the "speeders" down.
I do agree tho, something that takes 1.4b to "start" achieving, should not just simply be nerfed without warning.