With tokens and rng you end up playing for a good amount of time to get all parts, longer if rng is not with you. With the items as a quest reward the amount of time needed to get them would be to short so they had to add steps that would drag out play time to the max. With tokens your just grinding over and over to get that chance of a drop you want, the quest has to be done this way to ensure playtime is just as long.