One good reason why Play Along Keys is free to play

This is the main reason why Play Along Keys is free, particularly since sometimes kids are users. When app developers are part of most advertising networks, we have limited control over what ads might run on our app. We don’t want parents to have to worry in any way about what their kids might encounter on Play Along Keys.

Exclusive: YouTube ran ads from hundreds of brands on extremist channels

http://money.cnn.com/2018/04/19/technology/youtube-ads-extreme-content-investigation/index.html