I believe most of us are living a "Google Bubble". When we are online, our exposure to knowledge on a topic is limited by Search algorithms, personalizations, the availability of content that is digitized and searchable, etc. The people who comment on discussions, who creates content, etc. are also subject to this bias. This slice is not really the same as the larger body of collection of knowledge and insights about a particular topic. Even considering the limitation of knowledge that is digitized, there are plenty of sources that are not accessible and searchable (papers, talks, radio programs, conversations, personal anecdotes etc.). Books give a window to this larger world. This is the way we have done it for 5000 years. Books, in case of non-fiction, are written by people who have spent significant (sometimes their lifetime) time learning about a topic. And I believe the same logic applies for fiction. The ideas and imaginations of whole of human kind is not same as those of people who devotes time to create content online. In short, books are a different way (and arguably better) to expand your horizon.