I have noticed the same, especially with some users than just post videos.
Perhaps because in youtube almost anyone reply to comments, then they believe steem is the same, post a video and then forget about it.
With articles I do see more engagement.
Yeah, it does apply to videos an youtube effect, but as I've mentioned some are authors from antimedia or other sites, and they post their content here too, and they still don't reply. I checked their work on their original sits too, and they don't reply to comments there either.