Google will automatically delete all Android backup files that users save to their Google Drive account if the phone is not used for two weeks.
Google will detect the idle period of an Android mobile phone and start a 60 day count that if it zeroes it then automatically deletes the old backup of Android from the user's account.
Auto-delete function discovered this week a Reddit user who tried to retrieve a backup for the Nexus 6P that he had and that has experienced a problem. The user sent the phone back for repair and after being returned, he noticed that his phone's backup files had been flagged for deletion.
The page Google help offers very little information about this mechanism. Google does not show any warning about the auto-delete mechanism when users save a new backup. and does not send an email when the files are marked for deletion.
In brief, Google's backups include very sensitive data such as apps, call history, device settings, contacts, calendar, SMS (in Pixel phones only), Photos and Videos (Pixel phones only).