Ask Lemmygrad

You are correct, but to nitpick a little:

Apocalypto takes place in Maya territory, not in the Valley of Mexico. Though the depiction of sacrifice here is still inaccurate as the Maya didn't perform nearly as many sacrifices as the Aztecs did - I think they only ever did one per ritual or something like that.

IIRC the creators' rationalization was that people were scared and angry and the ruling elite were trying to calm them by just lopping off as many heads as possible out of desperation because of how bad things were, which from a narrative standpoint does kinda work but also would've made more sense in the context of Aztec society than Maya society and still feels more like it was more for dramatic effect rather than trying to be true to history. Not an impossible development but a very unlikely one.