I pick and I choose, selecting the books that appeal to me most. If I were a full-time reviewer, I could do one book a week. Young people in science don t like to do reviews, even in their fields of specialty. They are much too busy with their own work. Moreover, the science profession and the funding agencies give them no brownie points for writing reviews.
Reviews are simply one way in which demand is created for a book.
There are numerous other ways. Authors signings and readings in local bookstores. Discount houses lists and mailings. Reviews and descriptions placed on Web sites are suspect they were almost surely written by the authors themselves or by the publishers. Speaking from my experience as an author, I would say that publishers do a fine job with the editorial and production processes.