Similar way that Apple charges you to make free apps with their $100 fee.And Microsoft charges you (the developer) to release free Xbox apps?
There are no fees to apply to ID@Xbox, to submit a game to certification, publish, or update your games. There is a very modest one-time cost associated with development for the Universal Windows Platform.

Independent Developers Program for Xbox One | Xbox
The ID@Xbox program enables qualified game developers of all sizes to unleash their creativity by self-publishing digital games on Xbox.
www.xbox.com