Zip files are an example of something that works, are used extensively, and have a number of weird design decisions. Some of this just history, other not so much. But good luck replacing them for customers or friends.

They have some cool advantages. Like being able to read directly from the archive without decompressing the whole thing, per file checksum, and skipping compression on parts which won’t benefit. You can also wedge large amounts of arbitrary data into the file without changing it which… is kinda weird and sometimes useful?

Nasty bits are they used 32 bit ints all over the place, so rely on hacks to support larger files. Can’t support true streaming decompression. Implementations can vary quite a lot, as can compatibility. They also have a number of old and weird features that people don’t really use. Like being able to split a zip file into multiple parts, some ancient compression techniques etc.