Rickets has never and will never be eradicated. To begin with, it can be caused by diseases such as endocrine parathyroidism, hypoparathyroidism, hypocalcaemia, pancreatic insufficiency, chronic renal insufficiency, Fanconi Syndrome, certain drugs eg phenytoin, fluoride intoxication and aluminium intoxication. With regard to the latter, a good example is Camelford.
However, leaving all the latter to one side, there are other reasons Rickets will remain endemic. Lack of sunlight during November through March in certain latitudes (above 40 N and below 40 S) can cause the disease as can related issues such as complete skin covering by furs and other insulating clothing. Another cause is infrequently, people may have a mutation in 1 -hydroxylase, the enzyme that catalyzes the second and final step in vitamin D activation, or a resistance to vitamin D action in the tissues caused by mutations in the vitamin D receptor. The latter has to date, defied genetic manipulation.
Incidentally, the list above should not be taken as exhaustive - there are other reasons and conditions from which Rickets develops.