The Pokémon Company has announced that the Pokémon Jukebox app will be discontinued on Google Play as of June 30th, 2016. No official reason for the app being discontinued was revealed but the high cost per track seems to be the main cause. The app was free but tracks cost $0.99 for single tracks and $1.99 for medleys. The Pokémon music is significantly cheaper on CD's or via iTunes. The app only lasted approximately a year on Google Play.

Press Release

As of May 31, 2016, the Pokémon Jukebox app will no longer be available for download via Google Play, and new music will not be available for purchase. This includes re-downloading the app if you have deleted it or have changed devices.

Then, as of June 30, 2016, all other service for the app will end. You will still be able to launch the app and listen to any music you have already purchased and downloaded. However, you will not be able to download any music, including music you have erased.

Sources: http://www.pokemon.com/us/app/pokemon-jukebox/ and http://www.pokemon.co.jp/info/2016/04/160428_pc01.html