The article touches on this a little bit, I think.
Eve's eggs were harvested, incubated (though it turns out only the first 30 were fertile) and became the foundation of the zoo's new population of walking sticks.
I am not a real biologist, but I suspect it is some combination of the factors you suggest and that their genome may be simple enough that most defects make the eggs nonviable.
Insects also have complex genomes. The egg fertility most likely has to do with other issues (differences between the natural habitat and captivity, maybe there is a natural tendency for not all eggs to be fertile, etc)
Eve's eggs were harvested, incubated (though it turns out only the first 30 were fertile) and became the foundation of the zoo's new population of walking sticks.
I am not a real biologist, but I suspect it is some combination of the factors you suggest and that their genome may be simple enough that most defects make the eggs nonviable.