Robots have a hard time recommending unpopular items because they lack the context to differentiate between and good and bad. They'd have to be able to listen to music and make cross-referencing judgments about quality. Are the musicians playing well? Are the lyrics any good? Is the style original? Is the recording good? Is it cheesy? Does it try to imitate another song? Is it a good cover? Does it work in spite of a lot of negative indicators? Is it a nice complement to the songs before and after? etc.

But if you want to find hits in a genre + time period that you don't know very well, recommendation engines are pretty good, and you don't need to have DJs for that.