> why did filesystems never make the cut to become a cross-system standard?

Many reasons, the most important being patents and insistence by vendors to keep stuff proprietary (exfat, ntfs, HFS, ZFS).

Also, there are fundamental differences on the OS level:

- how users are handled: Unices generally use numerical UID/GID while Windows uses GUIDs

- Windows has/had a 255-char maximum length of the total path of a file

- Unices have the octal mode set for permissions, old Windows had for bits (write protected, archived, system, hidden) and that's it

- Windows, Linux and OS X have fundamentally different capabilities for ACLs - a cross platform filesystem needs to handle all of them and that in a sane way

- don't get me started on the mess of advanced fs features (sparse files, transparent compression, immutability of files, transparent encryption, checksums, snapshots, journals)

- Exotic stuff like OS X and NTFS additional metadata streams that doesn't even have representation ín Linux or most/all BSDs

And finally, embedded devices and bootloaders. Give me a can of beer and a couple weeks and I'll probably be able to hack together a FAT implementation from scratch. Everything else? No f...in' way. Stuff like journals is too advanced to handle in small embedded devices. The list goes on and on.