Klaus can only make his hybrids from werwolves because werwolves are not "made" they are "born." Meaning if a werwolf bites a human they will not become one, rather the gene is passed down from generation to generation. that is why there are so few of them. On the other hand to become a vampire you need to feed someone blood and kill them. So anyone can become one. So Klaus cant make vampires have a werwolf gene but he can make werwolves into vampires.