There's a split between the world outside of Alexandria and Alexandria itself. Outside, where the Zenith phenomenon is less prevalent, there's still been a softening/diversifying in tastes because the range of what's considered "average" has been expanded to a huge degree. The smaller end of the scale still exists, but standards have adapted to be more accepting and supportive of plump/muscular/very shaped figures, with people only really batting an eye when you start going towards the more extreme ends of the scale.

Within Alexandria there's a pretty clear attitude of "bigger is better", with Alexandria, being a manifestation of excess, hedonism, and horny, using her influence to promote an agenda of making women fucking gigantic in one way or another. While not every woman in Alexandria is a Zenith, "The Bigger City" and its various organizations and businesses encourages growth, whether it be in weight, height, muscle, curves, etc. so size in one form or another is often, if not universally, seen as admirable.

I'm sure the ideas you mention will be touched upon at some point if I keep up with the writing, which I probably will. :V