i think he wanted to name his book another name because the word night is just simple we need like a decent title.Another reason he might change it because no scene was at night.The last reason because the story was mostly sad and heartbreaking.He wanted night so he want the reader know its a dark sad book by the title.Another reason why the book is called night because it probably it means his dad died at night.The last reason is that  the book night because you don't see light barley in the Holocaust.

the reason why the book is called night because you don't see happiness in the Holocaust and it is nothing but depression.the reason why it wasn't the other title because it doesn't make sense because it doesn't bring a message into the book.