HBO films made a truly amazing movie called Too Big To Fail (The title is a link to IMDB, by the way,) which is, given that it's literally an entire movie about middle-aged white guys talking about economics, a stunning, gripping, dramatic film.
And it features a wonderful explanation of what really caused the crash. It's dramatic, it's funny, it features a terrific cast, and it tells you, step-by-step, how and why the economy did the catastrophic Brody it did.
Here's the scene, but, by all means, find and watch the movie. It's pretty terrific.
And that's why we're all fucked.