What are those reasons, if you wouldn't mind elaborating?

They both reflect the view that there is an objective, timeless, cosmic order --- perhaps related to the golden section or some other slightly mystical thing -- which allows them to state that some forms (the gentleman's dress suit, the "natural city") are inherently better than others.

I'd have to say I agree with that.

Yes, but without the refinement of certain key forms that have proven more worthy than others over centuries, there wouldn't be a coherent culture for hypereducated barbarians to sneer at.

Besides, buildings are habitats: our very biology influences the forms they take. If a style of architecture causes distaste or unease in the majority of creatures it is meant to shelter, then convention may not be the only factor at work. If you want radical new forms ad nauseum/infinitum (your pick), you may need to change the fundamental nature of the species for which it is intended.

Working within and against limitations invigorates and challenges; complete freedom and endless novelty is a prison, and ultimately a bore.