I don't equal “civilized norms” with hierarchic societies. At least in the case of IVC (Harappa, Mohenjo-daro, etc.) it was a full-fledged civilization comparable with Sumerian city states (collect-and-redistribute sustenance organization, populations of 20-40K people per city with highly developed culture, etc.) and it lived side by side with the hierarchic model until c. 1300 BCE (i.e. contemporary of Sumer, Akkadian and early to old Assyrian empire), sporting essentially the same culture sans polytheism and hierarchic social structure. Not to mention that IVC had extensive trade contacts with those hierarchic societies in Levant. Furthermore, Puebloans were/are a return from Mesoamerican polytheistic hierarchy to an egalitarian animistic social structure (and here we are talking some measly 500 year ago, IIRC).

Ironically, IVC collapsed and was replaced by the hierarchic model with arrival of Indo-Europeans who came from Levant. I would explain this by the dynamic that I could witness when socialism fell in central Europe. After the collapse of Iron Curtain, there was a very brief period (I'm talking months) of anarchy in some countries. Many people associate anarchy with chaos, but it could not be farther from the truth. In reality it's just lack of established power brokers. However, in this power vacuum, people without moral restrictions grabbed the opportunity and basically usurped power. What followed was the infamous “Wild East” mafia period of '90s and early new millennium. Well, as far as I can tell, a small group of people (few dozen) can essentially rule over a city with population of c. 35K. It's enough that they have no qualms killing and stealing. The “meek” masses essentially won't resist. Basically due to fear, but, subsequently, also greed.

To sum it up, the ideas of hierarchic social structure were well known throughout the IVC, but the hierarchy itself had to by physically imposed. That also answers, or at least hints at an answer to your question. I bet on education and, ultimately, absolute self-knowledge (aka self-realization, aka enlightenment). The rest will follow.

https://medium.com/@senderspike/social-restoration-530d3d8d2d3f

https://senderspike.medium.com/solarpunk-and-beyond-6ecb8a7a510a