Three years ago Miley Cyrus had the most streamed song on the planet. This month her new single fell off Spotify's global chart in three days, and the album behind it is tracking around 40,000 first week units, on pace for the lowest debut of her 20 year career. Those two numbers were never as far apart as they look. Flowers hid the gap. Flowers was a cultural moment. A divorce anthem that pulled billions of streams from casual listeners who were never going to buy an album or a ticket. In…