That's the trick with the humanities - they are not hard sciences, there is no canonical body of knowledge to be passed on; This isn't a straight download. Many things are a matter of perspective, of experience, and of particular schools of thoughts - all of the above poorly communicated via mere books.
That's the difference between a history book vs. a good history professor. Even without the (invaluable) ability to interact directly, it's the difference between a dry recounting of facts vs. more profound linkages into other areas of the field, or entirely other fields of study altogether. Sure, by reading books you will make some of these connections yourself, but it's hardly as good as what you'd get in classes.
That being said, there are certainly bad profs who do just do the dry recounting of facts, in which case you are basically better off reading the textbook at home. The presence of these should in no way discount the enormous positive influence of college educations done right.
My undergrad humanities courses were 100+ students packed into a giant lecture hall listening to a professor talk. There was essentially no interaction.