Why does my book have so many pages?

With Single-sided on, every design gets a blank back, so 30 designs make 60 pages, plus the title and copyright pages, the front pages (also on right-hand pages with blank backs), the answers at the back (four to a page) and the thank-you page. Turn Single-sided off to print designs back to back and halve the design pages. KDP has no single-sided setting of its own: the blank backs are real pages of the PDF and count in the printing cost.