People halo around the most visible artists. The various services promote the most popular artists, because that's what their audience wants. As the model shifts from a lean forward (I buy music that I like, so that I can listen to it) to a lean back (curated, data/discovery) model the top line hook for fairly un-engaged music consumers means that they discover less new music and hear more of what they expect to hear. Which is exactly what happened to radio, for exactly the same commercial reasons, over the past couple of decades.