Well another reason could be the temperatures... It's really not the season to be breeding. Most breedings start in october and go through early year. I know here in so cal it's way too hot to try introducing the males to females. Your best bet would be to just wait til the colder months, keep feeding them and getting them nice and big and trying again later in the year.
I do know of some breeders who breed all year long but that's because they have precisely controlled environments that give optimal conditions for this.