And it's not obvious that people want to discover art the same way they want to discover information (obviously not implying that Google can't be used to discover art).
HBO will never scale itself beyond it's own ability to comprehend itself, or, if that happens, it's quite a ways off. Considering HBO is throwing hundreds of thousands of dollars at each of these shows paying twenty bucks for manual curation on top of that doesn't sound unreasonable.
HBO is operating on a much more tractable problem. Human curation may work better here.