What's version of Moodle?
How much free space does your server have?
Do you have command line access to the server via ssh?
Reasons asked ... could have recyclebin in play.
If you have command line access, one can do their own thing with backups ... in admin/cli/ there is a backup.php script which allows you to backup a course by course ID *and* point the backup to a designated directory ... one that you can see.
That script takes course default backup setting - settings like keep users or not ... keep events or not ... etc.
I've had to resort to using that CLI script due to a course whose size was 130G plus and that would 'upset' auto backups every time and no way to exclude it.
So if you have CLI access be glad to share how to create a looping bash shell script that would backup every course from a cids.txt file (course ID numbers) and point those backups to a designated directory (which has to be manually created in advance of running script).
Even share the query of the DB from the command line to create the cids.txt file.
There is also a way to run that script with 'nohang up' ... which means it puts processing in the background of your shell session ... and will run until complete - allows you to log out of the ssh session so you can sleep!
'SoS', Ken