The reason has something to do with the fact there are so many other information sources that command my attention. I wasn't able to articulate this very well at the time, and now I don't have to because Scott Karp has clarified it admirably. The crux of his argument is summed up by these questions:
Yup, that's it (almost).
What if I do all my reading on the web not so much because the way I read has changed, i.e. I’m just seeking convenience, but because the way I THINK has changed?
What if the networked nature of content on the web has changed not just how I consume information but how I process it?
What if I no longer have the patience to read a book because it’s too…. linear.
We home-schooled our three kids for many years. One of the key advantages of unstructured home-schooling over scheduled learning in a classroom is that you can take advantage of the "learning moment". There comes a time when the child asks a question or otherwise lets you know that she is receptive to hearing some information about a specific topic, right now. The amount of learning you can pack into that moment is incomparably more than what gets absorbed from a steady stream of linear information going by.
Call me ADD if you want but I prefer to think of our digital age as enabling a rich variety of learning moments. Mommy isn't around to answer my questions, but Wikipedia is. So is Twitter, Google, the electronic editions of The Vancouver Sun and The New York Times, Safari books online, my social graph, etc. etc. Sure I hop around from topic to topic and can't follow the bread crumbs back to where I started sometimes, but on the whole I am getting more out of it than by following a linear track. Much more.
I disagree with Scott on one point. I don't believe his (or my) style of thinking has changed. Human thought processes are naturally nonlinear and hyperlinked. It's just that now we have information sources that match. Physical books that are read from beginning to end don't fit.