I would think its more related to royalties.. 'up and coming artists' are also cheap artists. I would am interested in subscribing to such a service for my properties.
FWIW, it was this song. Sounded amazing on the store speakers. Even today, it barely has 100k views - https://www.youtube.com/watch?v=2EdGEqbwSQ0
That said, of the two playlist selection companies that I have only just read about, the charge for streaming in-store is between $34 to $199 per location per month.
[1] Soundtrack Your Brand, a ‘Spotify for B2B’ nabs $22M for expansion - https://techcrunch.com/2017/02/17/soundtrack-your-brand-a-sp...
[2] Restaurant music emerges from the background - http://www.crainsnewyork.com/article/20170807/ENTERTAINMENT/...