Human sacrifices were observed by the spanish yes, but that wasn’t the reason why they decided to conquer the Aztecs, in fact, I’d say that was barely taken into consideration.

I'm not an expert but it probably never factored in. The conquista was actually a lengthy process of forging alliances and subterfuge between the spaniards and the indigenous peoples who felt animosity towards the dominant aztecs. The brunt of the conquistador army was comprised of native conquistadores, which are exactly what you think they are. Some even enacted campaigns independently of the spaniards. And once the process was consumated, native conquistadores were offered a portion of the spoils and some positions of power, they become caciques and collected tribute to the spaniards. Slowly but surely indigenous peoples adapted to the now dominant european power and became assimilated. The process is infinitely more interesting than the boring eurocentric version of "the spaniards were venerated as gods and absolutely crushed the aztecs with their mighty steel" where the spaniards were motivated by fixing these goddamn backwards people.