I just read your other post, Those are the breeds I would like to get next. Pretty birds.
I think it is random. Something causes the infundibulum to fold or get caught and it misses the corpus luteum.
hatchery stock would be my biggest guess as to why. They do not get to see their offspring grow up, so there is no culling of a producer that has chicks with issues.
There you go Eggsy...using those big words on me! Hatchery stock seemed to me to be a common denominator among some of the posts I read (and definitely my own). Something Speckledhen mentioned that made sense was to the effect that hatchery stock is bred for egg production and not for longevity.
Which brings me to another question...how do you know if you're dealing with a "hatchery" vs. a "breeder"? Are there industry standards or regulations required to be classified as one or the other? Can anyone call themselves a breeder? If regulations aren't in place, how would someone know (at least someone like me) they weren't getting hatchery stock from someone that calls themselves a breeder?