[barneygale]

Most of the alternatives you suggest are implemented in PAX, which is an extension of the tar format. The EoF block is useful if the archive is written directly to physical media without a filesystem: it lets you determine where the archive ends.

[vitiral]

Wouldn't such a feature be better put on the physical media controller/protocol itself?

[h2odragon]

yes; but then people wanted to be able to read the tapes they'd written long before the hardware and media acquired such features, so TAR kept the ability (it was more don't change things that aint broke, i think).

ARC and ZIP files are written as a fresh take on the idea of archive files, with much more capable hardware, after TAR had been around a couple decades. They have many features designed to use those new hardware capabilities, and were (and still are) very popular because of those.

They have bits that probably seem dated now, too. Breaking archives into floppy size chunks? but without any sort of forward error correction? No format support for unicode? (who cares it wasn't invented when the ZIP file spec was created?)