Why have the aztec ruins in mexico city not been dug up?

The Aztec ruins in Mexico City had not been dug up due to the archeological sites being so close to modern-day infrastructure. Excavation would have to be done slowly as carefully due to modern sewers, pipes, and subway rails. Also, the Aztec capital was built on a lake bed and has to often be pumped out when the areas flood.  

- "ethical issues. deception – the participants actually believed they were shocking a real person and were unaware the learner was a confederate of milgram's. however, milgram argued that “illusion is used when necessary in order to set the stage for the revelation of certain difficult-to-get-at-truths.” "

- "milgram's work was conducted in the early 1960s before the current.the studies ignited a debate about the ethical treatment of participants. what appear to be dangerous, if not deadly, electric shocks and the by today's ethical standards, many questions about the research have gone unanswered."