Because the embryo pictures that he shows are essentially correct. Vertebrate embryos do indeed resemble each other at the phylotypic/pharyngula stage of development, and that is indeed a powerful argument for evolution. What was “fradulent” about Haeckel’s embryos was that they were a little embroided to look a bit more similar to each other than they really were. They’ve now been replaced in textbooks by photographs of real embryos showing essentially the same thing. And, of course, the entire field of embryology has been revitalized by combination with molecular biology and genomics to form the field of EvoDevo —- an incredibly important area of science today showing correlations between development and evolution only dreamed of by people like Haeckel. But Jonathan Wells doesn’t write books about that —–