/u/drylaw and /u/611131 have previously answered Why did Hernán Cortés destroy Tenochtitlan and build Mexico City right on top of it?

Drylaw and /u/400-Rabbits have also explained why Lake Texcoco was filled with dirt in the 17th century.

​

EDIT: 400-Rabbits was interviewed on an episode of the AskHistorians podcast about Tenochtitlan and Tlatelolco, as well as about the Aztec Conquest near the podcast's beginning: (part 1) and (part 2)