Why did God undertake to protect the Holy Qur’an from distortion, while He did not undertake to protect other heavenly books from distortion?

Faith is based on submission to Allah's command, contentment with His decree, and the belief that what He has legislated is founded upon perfect wisdom, and that He, the Exalted, "is not questioned concerning what He does, but they will be questioned." Perhaps one of the wisdoms behind preserving the Quran, unlike other books, is that the Quran is the last of the books, and Muhammad (peace be upon him) is the last of the prophets. Thus, its preservation from alteration was fitting, due to the absence of another prophet to be sent to negate any distortion, unlike the previous books, after which other prophets came.