Classicly

Baby books were not written to teach parents how to care for their children; baby books were written to sell baby books. And magazines published articles about babies to sell magazines to mothers.

Valid reasons. If they had not existed, there would have been no baby books, no women's magazines. But this had far-reaching consequences: the market for baby books and women's magazines was the great, proliferating population of new parents. If the awful truth about parenthood were published, if these hardy, ingenuous souls were discouraged, something quite startling would happen to the market: it would disappear.