IBM's i Series, modern heir to OS/400 doesn't have a "filesystem" in the traditional sense (but tons of tools to emulate and approximate it). Everything ends up in DB2.

I've spent time crawling around the SCSI/SAS/Storage of systems like that. Wrote dirty hacks for end-user clients to cope with incompatibilities. EG multiple versions with the same filename are totally fine. Filenames needn't and aren't unique in such systems, just another col in the DB. How do you tell a Windows ftp client which of the 20 different "report.txt" files it should download? (Filezilla actually has 'VMS' options for this, its more common than you think.)

If all you ever deal with is relatively simple, well defined, CRUD type applications on entirely abstract systems in some remote infrastructure, its easy to think that's how all development should look. It doesn't and it shouldn't.