Muscle memory. We've been doing gzip for decades and we are too lazy to remember the zstd commands to tar, assuming the installed version of tar has been updated.
That's cool! Is that a GNU tar only thing? Based on it being a longopt, I'm guessing a GNU tar only thing. That's the problem with these things, it takes a while to get pushed to all the installed copies of tar running around. Perhaps it's time to check:
* MacOS Sonoma(14.6) has tar --auto-compress and --zstd
* OpenBSD tar does not appear to have it: https://man.openbsd.org/tar
* FreeBSD does: https://man.freebsd.org/cgi/man.cgi?query=tar
Both libarchive ("bsdtar") and GNU tar have -a, which I guess are the only two upstream tar implementations that are still relevant? You're right, it can take a while for these things to propagate downstream though.
Ooh interesting. I'd assumed (incorrectly) that OpenBSD tar was just libarchive like FreeBSD and NetBSD. I prefer BSD libarchive tar to GNU tar as /bin/tar on my Linux machines too for what it's worth.
OpenBSD is fairly brutal on allowing third party dependencies into base. I'm sure there is a package for both libarchive and gnu tar(Haven't actually checked, but I'd be surprised if there is not).