1. Scrolls were more difficult to handle as you read.

2. You could jump around to various places in a long book document, but with a scroll you had to manually unravel it to the point you were looking for, a time consuming process.

3. Books were not without their difficulties, however: http://www.youtube.com/watch?v=pQHX-SjgQvQ

But in all seriousness, the scroll concept works perfectly well, in fact better than the book concept, provided you have the right technology to drive it. And modern computers have that technology. I can use a search box to jump to wherever I want. I can quickly scroll up and down in the document using a scroll bar rather than paging through a book.