I'm mostly in the pro-written word camp myself, but I have sought out video tutorials in cases where written docs seem to assume something I don't know. When I'm learning something new, a written doc might have a 3-word throwaway clause like "... add a user and then...". But I've never added a user and don't know how. If it's niche open-source software with a small dev team, this may not be covered in the docs either. I'll go fishing for videos and just seeing that they go to a web-ui or config-file or whatever sets me on the path to figure out the rest myself.

That is to say, video content that shows someone doing a thing successfully often includes unspoken visual information that the author doesn't necessarily value or even realize is being communicated. But the need to do the thing successfully on-screen involves documenting many small/easy factoids that can easily trip someone inexperienced up for hours.

I'm as annoyed as anyone when I want reference material and find only videos, and I generally prefer written tutorials as well. But sometimes a video tutorial is the thing that gets me oriented enough to understand the written worthy I wasn't ready to process previously.

Edit: The ubiquity of video material probably has little to do with it's usefulness though, and everything to do with how easy it is to monetize on YouTube.