I never worked in search, curious what are the technical difficulties of implementing a YouTube-style "Don't Recommend This Channel" are? From the outset, the Y

I never worked in search, curious what are the technical difficulties of implementing a YouTube-style "Don't Recommend This Channel" are? From the outset, the YouTube recommendation can be an offline process, and much easier to scale. Google pretty much has "F-you" level developer man-power to throw at this problem, so I'm somewhat surprised they haven't implemented it yet (the "bad result is good for Google" reasoning never quite made sense to me). I'm curious if the functionality is not worth it or if the technical challenge is insurmountable at Google's scale.