Looks very much like a format that should just have been gzipped JSON.
Don't use binary formats when it isn't absolutely needed.
Don't use binary formats when it isn't absolutely needed.
Also, it's a format designed to hold binary data. JSON can't do that without hacks like base64 encoding.
Binary file stores like this are very common in highly optimized software, which operating systems tend to be, especially if you go looking at the older parts. Windows has a similar format embedded in EXE/DLL files. Same concept: a kind of pseudo-filesystem used to hold app icons and other resources.
For application file formats that require storing binary blob data such as images, bitmaps, etc , many in the industry have settled on "SQLite db as a file format": (https://www.sqlite.org/appfileformat.html)
Examples include Mozilla Firefox using sqlite db for favicons, Apple iOS using sqlite to store camera photos, Kodi media player uses sqlite for binary metadata, Microsoft Visual C++ IDE stores source code browsing data in sqlite, etc.
Sqlite db would usually be a better choice rather than binary blobs encoded as Base64 and being stuffed into json.gzip files. One of the areas where the less efficient gzipped JSON might be better than Sqlite is web-server-to-web-browser data transfers because the client's Javascript engine has builtin gzip decompress and JSON manipulation functions.
Sane for 3rd party devs
I personally subscribe to the Unix philosophy. There are really two options, binary or plain text (readable binary due to a agreed standard formatting). All other formats are a variation of the two.
Additional a binary format suits makes sense when the format is to be used for mobile devices which may not have much storage or bandwidth.
JSON in particular isn't very good [0] but I'd also argue that text formats in general aren't great. Isn't it a lot better that an int32_t always takes exactly 4 bytes instead of anywhere between one and eleven bytes (-2147483648)?
Computers need to do it a bunch for every program launch for every single user of macOS for decades. The developer just needed to write a generator and a parser for the format once.
Would it have been a bit easier to write a parser for a format that's based around a zip file with a manifest.json? I don't know, maybe. You'd end up with some pretty huge dependencies (a zip file reader, a JSON parser), but maybe it'd be slightly easier. Is it worth it?
Why not have both options? .gltf and .glb being possible for assets been more than helpful to me more than once, having the option gives you the best of both worlds :)
Working with binary files really isn't that hard. If Apple documented the .car format, writing your own parser wouldn't be difficult. It's not like it's a complicated format. Still, Apple clearly doesn't intend for people to make their own .car generators; to them, ease of reverse engineering is a bug, not a feature.
Using JSON / HTTP for backend communication (i.e. microservices) is madness when you consider how much overhead there is and how little value having it be human-readable delivers.