Giants continue to grow for a couple more months.... he is still a baby yet. To get to max size... you have to do the max work. Means significantly larger grow out... many water changes.... feeding 4-5 times a day (and because they seem more sensitive you have to give a variety).
The breeders don't want to log in any more time than 3 to 4 months. Time is money and to raise a fish for 8-9 months till they reach max size is not a sound strategy business wise. (Not to mention shipping prices would also be majorly effected.)