One of the most important things to learn about publishing is how to properly submit materials to editors.
Sure, some editors are pretty informal and will look at whatever is sent. But, the vast majority of editors are incredibly busy, and they won't bother looking at anything that isn't at least close to being properly submitted.
For a non-fiction book proposal, editors expect to see a book proposal. For a work of fiction, they want to see the entire manuscript. Why? It's pretty simple. A non-fiction book proposal explains the book concept, the author's credentials and lots of other important information in a "snapshot". Usually in non-fiction the author's credentials as an expert are important.
In a novel, the ability to tell the story from start to finish is crucial. Thus, editors just want to read the story—all the way through.
Non-fiction book proposals are very formulaic—a lot like prescriptions. Imagine if you wrote out an Rx for the pharmacist that said, "Hey, give this nice lady something strong for her high blood pressure." What do you think would happen? Well, trying to get a non-fiction book published without writing a proposal is a lot like that. It's just not going to work very well.
I write this (and all of my future blogs) with the caveat that no matter what I say, there are writers out there who will prove me wrong. That's because there are ways to do things that aren't very conventional. But, usually it's eaiser to go the conventional way and just get the nice lady the Rx you want her to have and get book editors to take your proposal seriously!