Why is only Quran protected by Allah and not Bible or Torah?

Salam , Quran is the un-altered word of Allah. Allah had promised for the protection of Quran. We also believe that Christians and Jews corrupted the Bible and Torah for their personal profits. I want to know that why did Allah only promised protection of Quran and not his others books? Why didn't he saved other books from human corruption, like he's doing for Quran?