Video is a really hard medium, I've always thought. It's harder to monetize than writing, and takes up a lot more time. You can always edit sentences easily (or re-arrange the pics if you're writing a tutorial article, etc), but editing video takes more time, especially if bits need re-shooting.

As the article says, the people who are willing to put in the time and energy and effort are often people who tend to be attention-seeking. I don't mean that in a bad way, just that to do it and to enjoy doing it, you need to have some sort of non-monetary incentive in some way while getting started as a YouTuber, and I can see how someone who is attention-seeking would like it more than someone who is an introvert.