People aren't going to watch variations of the same content back to back, but they do want content presented in a fairly consistent way that draws their attention.

YouTube also penalizes creators from straying too far from their typical content, encouraging separate channels if they want to make diverse content. So that encourages creators to carve out a niche for themselves and fill it. Users will gravitate toward the "best" in a given niche (for various definitions of "best"), so there's pressure on creators to get better at whatever their unique niche is.

If you really look at YouTube, you'll find a huge variety of content with high production value that follow a similar marketing style (thumbnails, titles, and presentation format). The marketing style being similar doesn't mean the content is similar.