As you observe a sin being committed, do you ever exclaim, "the world is surely a better place now that this sin has been committed!"? If you answered "no," know that unlike you, Allah wants sins to be performed:
Abu Ayyub Ansari reported that Allah's Messenger (may peace be upon him) said: If you were not to commit sins, Allah would have swept you out of existence and would have replaced you by another people who have committed sin, and then asked forgiveness from Allah, and He would have granted them pardon. (Sahih Muslim, Book 037, Number 6621).
Why does Allah want people to sin, just so he can grant forgiveness later on?
Abu Ayyub Ansari reported that Allah's Messenger (may peace be upon him) said: If you were not to commit sins, Allah would have swept you out of existence and would have replaced you by another people who have committed sin, and then asked forgiveness from Allah, and He would have granted them pardon. (Sahih Muslim, Book 037, Number 6621).
Why does Allah want people to sin, just so he can grant forgiveness later on?