Your audio will generate revenue on YouTube based on:
- Each viewer's territory
- The placed ad format
- The viewer's device
- The user experience
To make sure each viewer has the best experience, YouTube does not place ads on every view.
There are also territory-specific issues. For instance, in Germany some of the videos containing your audio may not have ads placed on them due to a conflict between YouTube and German Performing Rights Organization GEMA, and is not related to YouTube Content ID.