Simple answer: because we need money to keep this website functioning, maintain the forums, and to pay all of our organizers and industry professionals.
Our website gets a very heavy volume of traffic, so we have to use web hosting that frankly isn’t cheap. We also believe that artists, writers, agents, and editors shouldn’t have to work solely for “exposure” or because of “passion,” but should be rewarded for their time, effort, and knowledge with something that can actually buy them groceries.
We know how expensive in-person conferences can be, having attended a few ourselves. You’re not just paying the conference fee, but also for the hotel room, meals out, plane fare or gas money, lost wages from your day job, etc. An online conference eliminates these concerns, and we always try to keep the conference itself affordable.