Conferences usually have a relatively small number of attendees. By recording the talk you can reach a much wider audience. For example: when I was in college I

Conferences usually have a relatively small number of attendees. By recording the talk you can reach a much wider audience. For example: when I was in college I used to watch lots of conference videos, even if it just had a few thousand views. If there hadn't been videos, I wouldn't have had any way to access the same content. Actually traveling to some of those conferences would've been prohibitively expensive at the time. Heck, even now I find most conferences to be prohibitively expensive.