Why didn't Allah SWT protect the other books from corruption like He did with the Qur'an...?

If Allah protected the other books, other prophets wouldn't really be needed because the people of the other nations would already know the truth.Allah does everything for a purpose, so what would be the purpose for the other prophets to say that someone after them would come? Allah says that prophets came to every nation and culture to prove that He loves every nation. In the Quran , not all the prophets were listed. God only listed the ones that we can learn lessons from. There were no need to because they all said the same thing but in different nations.One nation is not superior in the sight on Allah. The last was the Arab nation and it was protected. And in that book God said that He sent prophets to every nations in the world.