That's exactly what's going on. Pandora put a bunch of effort into analyzing each song by a bunch of characteristics: https://en.wikipedia.org/wiki/Music_Genome_Project. They then use that to recommend music that's actually similar, and not just "people who listened to this also listened to...." It's pretty labor intensive so probably not something that the other services are too eager to pay for. Maybe we'll get some facsimile of it from computer-generated analysis now that AI is becoming so capable.