That's because it is simply done. For the most part the only thing that really happens in a big way is that the background changes out based on scroll position.

That's because it is simply done. For the most part the only thing that really happens in a big way is that the background changes out based on scroll position. Any other element that animates on scroll does so in a minor and subtle way. The actual scrolling of the page is not altered in any way. I agree, this is one of the better ways to handle such things if it has to be done.