Most likely because the status of your questionnaire is Inactive
Each questionnaire can be set to active or inactive.
The status is displayed in the list of questionnaires in My Library.
If Inactive, you cannot use the questionnaire to create audits, and it will not appear in your list of available questionnaires when using your app on a tablet. This is also a way to hide (from the app) previous versions of questionnaires or those you have retired, or those you are working on.
If you click Edit for a questionnaire that is Active, the system will automatically change the status to Inactive. The system does not automatically re-activate the status, so once you have finished editing, make sure you set the status to Active. It will then be visible to you when creating new audits.