The thing thats wild about Tenochtitlan, as the story goes, is that the Aztec people discovered it themselves, and no one really knows who originally built it!
To most Americans today, who have no idea why their country works the way it works, and would rather tear it all down, I'm sure the actions of the last few generations might seem alien.
But also more broadly, your point is basically why Teotihuacan is so interesting to me! Not because of aliens, but because its fun to think about how the Aztec/Mexica people were as displaced from the origins of that particular place as much as we are!
But yes absolutely with you: even more so than attributing it to a particularly American decadence (which is a little too pat/editorial column to pass my sniff test, but ymmv), the whole impulse to Ancient Alienize things seems to me to be a kind of mystification which sustains, ultimately, racist/colonial stereotypes of ancient non-white people. It clearly serves to sustain a certain idea of civilization, rather than overturn or disrupt it.
Either way, its an important point, and happy to be your punching bag so you can make it!
Asking the question: "How could they have done that?" is not dissimilar from asking "Why didn't we do that?" so occasionally truly curious individuals do step through the self-soothing cultural narrative.
Considering that the Aztecs were a recent conquering group, the southern extremity of their ethnicity, that isn't surprising at all, whether or not it's true.