Why do authors wait until the last book to kill off characters?

[Jojo]

I can think of so many other books this happens in i.e. mockingly or allegiant. It is like you get so attached and move with these characters through multiple novels and are basically part of there lives for the whole ride and the author kills them off. Its like they want it to end in a bang but there are so many other ways to do that

[Kin]

I think they do it for emotional content. They want the reader to really feel the ending, the power of it. Yes there are other ways to do that, but seeing someone you've really grown attached to killed, is a new kind of heartbreak.

It's so predictable nowadays as well, I usually know who's going to die before the book is even over.

[Jojo]

I like going to the movies of books that were made into movies and whispering you die, and you die, and just really pissing my sister off