Perhaps ordinary citizens were repelled and terrified by what was happening. Humans have a deep sense of right and wrong. It doesn’t translate necessarily into those that are in power but like pornography people know even when they see it. I wonder when Cortez came, whether the citizens had the fight in them to defend what was probably a tremendously twisted and evil culture.
There was a reason some tribe eagerly joined the Spaniards to go after the Aztec.
Cortez had only a few guns and soldiers. But he served as the core for the revolt of all the natives oppressed by their rulers.
Cortez had no trouble recruiting natives of other tribes to fight against the Aztecs. Cortez, good Christian that he was, recognized this business as the demonic horror from hell that it is.