Right now I think the videos have all been from past What If…? entries. He’s already done the research, so to me it makes sense to use it again. Maybe some people prefer videos/audio to reading. Similarly, if he ever does new ones for a video, I assume he would also turn those in to written entries as well for the website. For him most of the work would be the research, so he might as well get as much use out of it as he can. I can understand doing exclusive ones for the books, though. He’s getting paid for those, so it’s worth extra effort.