The Aztec Religion was so sacrificial, so barbaric and full of idol worshipping.
Cortes wanted to do away with the worship of idols and making human sacrifices to them. Back in the days it was a very common practice of the Aztec people.
Cortes was able to conquer the Aztecs for many very different reasons. In these reasons allowed him to have the victory of Mexico. The various causes for Cortes' success begin with that the Aztecs had a harsh tribute system that was not popular among the people of Mexico. This cruel tribute system allowed Cortes to act as a liberator.