Is there any reason the discussion is inverted in e-mail threads?

In all e-mail clients I know, when someone is responding to an e-mail, the response is written at the top, above the original e-mail.

I don't understand the reason for this choice. It seems that:

  • For any e-mail which is long enough to require a vertical scrollbar, I have to scroll to the top before answering.

  • It makes it very awkward to read a discussion with several e-mails. I have to read a piece of text from top to bottom, then jump to the top and find the beginning of the next message.

  • It's simply counter-intuitive. Books, scientific papers and web pages are written from top to bottom. There is no such a thing as chapter one being positioned at the end of the book, and the last chapter being at the beginning.

What would explain this original choice? I mean, since someone, around 1985, came with the idea of doing it this way, as opposed to use a usual paradigm used for existent content such as books, there was probably a good reason for that. Or was it purely technical?