why did atahualpa order to troops not to fight the spanish

Answer 1

Francisco Pizarro told the Incan people that he would spare them their lives if Atahualpa's prison cell was filled with gold. The conquistador took the gold and killed them anyway.

Answer 2

He saw the Spanish as a small force, of little threat to him.

Answer 3

This article has your answer.

http://en.wikipedia.org/wiki/Atahualpa