What goes around
comes around.

All religions worth their salt attempt to fulfill three needs.

A bed-time story, a survival manual and a get-back-on-track strategy.

The bed-time stories depend on what had already happened before their respective inceptions. On the particular histories of the people entertaining those stories. On the respective cultures which have generated each of the religions.
The get-back-on-track strategies, again, depend on the specific social-psychological aspects of each individual civilization using a particular religion.
Unsurprisingly, given the consistent nature of the human being, the survival manual is the same.

Regardless of the specific wordings used by various religions, the core of each of those manuals is faithfully summarized by “what goes around comes around”.
Mind you, I’m speaking here about ‘successful’ religions. About religions which actually help the civilizations which use them to survive for sizeable amounts of time. About effective religions which create a collective mindset capable to cope with ‘the unexpected’.
For example, the religion used by the Aztecs had failed in their hour of need.

Do you have a better explanation for what had happened?
A very small group of lousy invaders – yes, the Spaniards led by Cortes were full of lice – being able to overcome an entire empire demands a better explanation than the technological differences between the two civilizations.
“Yet weaponry alone clearly would not enable Cortés’s tiny force to overcome a large, densely populated society of about twenty-one million. Quite apart from military technology, Cortés ’s expedition benefited from divisions among the indigenous peoples of Mexico. With the aid of Doña Marina, the conquistadors forged alliances with peoples who resented domination by the Mexicas, the leaders of the Aztec empire, and who reinforced the small Spanish army with thousands of veteran warriors. Native allies also provided Spanish forces with logistical support and secure bases in friendly territory.”

The point I’m trying to make here is simple.
The Aztec Empire observed a certain religion. They had to, in order to function as a state. As a social organism.
Which religion allowed (demanded?) the rulers to treat the general population in a certain manner. Which general population ‘made good’ of the first opportunity to rebel.
Little knowing that their new masters were no better than the old ones but …

The Aztec religion wasn’t good enough. Was unable to unite those who observed it into a community. Was unable to convince the believers to behave. To treat the ‘others’ in a respectful manner.
Was unable to convince its believers that ‘what goes around comes around’!

The idea wasn’t mentioned at all in the Aztec ‘bed-time story’?
The faithful stopped believing it at some point? For whatever reason?
The religious leaders had given up promoting the concept? In earnest? As in behaving like they were convinced themselves as opposed to merely paying lip-service to the ‘whole thing’?

Does any of the above even matter?
For us, trying to make sense of what had happened?