I'm curious as to how herniated nucleus pulposus develop?

Varies: There is a strong genetic issue meaning family history and higher in smokers and in certain activities such as those involving repetitive rotation with flexion especially lifting a load or a sudden lift of too heavy a load as well in those who are out of shape and do not exercise. Obesity also can be a factor and sedentary life style with age, there is an increased incidence due to disc aging.