Why Did Moctezuma Keep Cooperating With Cortés?

Si Sheppard thinks Moctezuma suffered a complete psychological break the first time someone else told him what to do, and then became Cortés's willing puppet.

Before the seizure, the records Sheppard cites show an autocrat who centralized power in the aristocracy and stopped outsiders from rising into the inner circle. He was turning ritual flower wars into campaigns of encirclement. Spanish accounts give him a regal bearing and call him clearly intelligent. After he was taken he learned Spanish quickly, and he learned cards and chess. Sheppard's reading is that he tried to do what Cortés wanted in ways that would still help his own people, without challenging Cortés. He treats as guesswork the idea that Moctezuma was waiting for a chance to rally his own side and simply never got it.

His own people removed him, because they decided he had sold them out. Being set aside like that had not happened before in Aztec history. He was the first huey tlatoani, the great speaker, repudiated by his own people and replaced by someone else.