Books and journals tend to have a wide distribution but a long publishing lead-time. For example it often takes more that a year for an article to be peer reviewed and published in a learned journal. Journals have a shelf life of about a month or so, and then can be hard to locate for study. Technical books have a long lead time, of the order of a year, but may have a shelf life or several years, however in general, they tend to sell relatively few copies unless they are widely adopted as college text books. The traditional face to face conference only lasts for a few days.
Conferences contain panel forums and paper presentations.
The panel discussions can provide the audience with information that is current at the time the panel takes place, however, once the session is over, the contents are lost to the world at large. Consequently ideas and methodologies published in conference proceedings do not received wide distribution. This results in a situation where the idea or methodology gets rediscovered every year or so, instead of being used as a basis for further exploration. In addition, conference peer reviewers may reject publishable papers because either the papers do not fit in the theme of the conference, or there were too many submissions for the few days of the conference. Advertising the conference.