The size of an author's single packet of output is shrinking. For that matter, so is the user's apetite for large books. As the value of time gets measured in sub-minute scale - who has time to read books? If you do, you are one lucky person, because I don't.
There are a lot of alternative media competing for my attention - TV, DVD/Video, Internet - each engineered to be more captive than the other. If before providers were after your money, now its your time as well.
It's a multi-tasking world, even in your spare time. After all, it is said we are only using upto 10% of our brains - so it can be deduced that nobody need care about an information overload.
I grew up reading books, used to be my favorite passtime. Best way I find to read a book is a quiet place or at most instrumental music in the background. It would also be good to have a tension-free hour. The fact that I have to work at creating that, shows me how much the world has changed. My modern multi-tasking nature does not let me sit still doing one thing - I feel too nervous, that I'm missing something else somewhere.
From the author's point of view, books take time, usually months to write those hundreds of thousands of words, formed into a coherent structure. Newer generations don't have that patience. Modern books tend to arise from a collection of previously published smaller articles.
Is it any wonder that blog site such as these generate so much more participation and output.