[notyourwork]

Perhaps its because its a niche that isn't worth investing the resources into? Sometimes narrow problem spaces are harder for a company to justify because of the cost to reward ratio. I agree with what you want and would like it myself for music (Spotify, Amazon Music, etc.) but it's a complex problem (recommenders, custom UI and the glue between) that is hard to justify compared to incremental small improvements to existing general purpose recommendations.