The Repentance - 9:70
Did not the news of those before them reach them, like the people of Noah, and the people of Ad, Thamud, and the people of Abraham, and the inhabitants of Median, and the inhabitants of the overturned countries (Sodom and Gomorrah)? Their messengers had gone to them with clear proofs. Allah was not oppressing them, but they were oppressing themselves.
Why a human messenger?
The Night Journey/17:95
"Say: "If there were angels inhabiting the earth, We would have sent to them an angel from heaven as a messenger."