This is not about protecting or not..
Allah tests us..and we were getting tested by channging the wod of Allah too also.. but again The Qur'an is the last book it has to be protected by Allah not having any change to let the people who live to close to end of the time.. so Allah will judge them too..and will say you had something from Allah but you did not believe.. or you believed.
That's why Allah protects the Quran.. Because it is the last book from Allah.