by Ken Task.
"why they don't appear"
Bug? (maybe) ... or it was thought that in the context of System Admin, not desired for teachers to see the backups of other courses.
"and where to find them in moodledata"
If you have setup a designated directory outside of moodledata and autobackup set to save there only, they are not in moodledata. Thus, one won't find them in moodledata.
Case where that's handy .... on a typical Linux server moodledata 'normally' in /var/www/ and main device/drive has only 30Gig - enough space to run a small moodle. But one has some massive storage device attached ... like a Google Bucket.
'SoS', Ken