The comparison to the hunter/gatherer stage is not really fitting as our live circumstances have vastly changed. We live in cities with thousands or millons of other individuals, even if we live in a rural area, going to the supermarket or something like that brings us in more contact than hunter/gatherer groups might have had in months. Thr advantage might be simple energy and resource costs to produce vitamin c. At some point, our nutrition covered the necessary daily intake enough so that there probably was no point anymore to spend bodily resources in producing it. Other mammals can still produce it, so it might have been intense, kind of knowledgable foraging (of course I know they didn't know about vitamin c, but they must have found certain plants are better than others) or agriculture, that brought us this way.