What do you mean "human powered" rather than ML? How are the implicit/explicit judgements of relevance (e.g. likes, clicks, views, star ratings) that are used in rec algorithms any less human than, say, a recommendation from a single trusted expert?

Personally I think it's amazing that even basic recommendation algorithms can instantly select 10 mostly relevant items from corpora of millions of irrelevant items. I think people are too used to receiving excellent recommendations and do not realise what receiving bad recommendations would be like. Hybrid systems such as Spotify's are really amazing when you think about it.