Amazon and Spotify and Netflix are all enormous examples of not just giving you what you asked for (->recommendation engines). They were there all along, just

Amazon and Spotify and Netflix are all enormous examples of not just giving you what you asked for (->recommendation engines). They were there all along, just less egregiously. Even PageRank (the secret sauce in the original Google search) is arguably a recommendation engine. You can just use PCA of some feature then use cosine similarity, this has been known forever.