This may be the impression, but it's not an accurate picture. The number of ebooks available from Sony have increased mostly in the categories of history, business, science and nature, and education and reference (as a percentage of where they were in September). Lately, these are rising at 3 to 4 percent per week. The totals for romance novels and mysteries and thrillers have increased only slightly. I monitor this every two weeks and maintain a spreadsheet of the totals in each category - for giggles, I guess. I post updates here:
https://www.mobileread.com/forums/showthread.php?t=16810 