Elon tweeted about it. Back in 2010-2012 when they were building the Model S, streaming music to a car over 4G wasn't that big a thing, and Slacker was really the only option available to them, Spotify wasn't. They entered a long term contract which is why they can't offer Spotify in the US currently. The only way to get Spotify in the US is to have someone root and hack your car to enable it, and even when it's enabled in the U.S. the next firmware update wipes it back out again. I have it on my car now... until the next firmware update then I have to have it re-enabled. Also, you have to use your own Spotify login, you can't use the generic Tesla one. It's much much more than just a cable. If so, that's great, and Tesla finally got out of their Slacker contract.