Bit unrelated rant but I'm still not sure why ZIP has been adopted as an Application File Format rather than anything else. It is a remanent of a DOS era with questionable choices, why would you pick it over anything else?

- archiver format to stow multiple files in one; your actual files (in your choice of format(s)) go inside

- files can be individually extracted, in any order, from the archive

- thousands of implementations available, in every language and every architecture. no more than 32KiB RAM needed for decompression

- absolutely no possibility of patent challenges

If all you need is a bag of named blobs and you just want quick reasonable compression supported across all platforms, why not?

If you don't need any table/relational data and are always happy to rewrite the entire file on every save, ZIP is a perfectly fine choice.

It's easier than e.g. a SQLite file with a bunch of individually gzipped blobs.

Because Windows can view and extract them out of the box without installing any additional applications. If it supported anything better out of the box I'd guess people would use that instead.

It works well enough. What could, for instance, epubs gain by having another base format instead?

I think most format use "gzip" instead of "zip".