why dont apple products support .rar files as default?

There are many compression and archiving formats available: https://en.wikipedia.org/wiki/List_of_archive_formats

RAR is a proprietary file format with paid, proprietary archive-creation tooling, while tools to extract the RAR archives are available from various sources including from the vendor: RARLAB.

Given the vendor restrictions on the archive-creation tools, I wouldn’t expect RAR support to become available as part of macOS.

If you need RAR support, download the tools from RARLAB.

Apple provides various tools for unpacking common archive formats, including tools associated with (optionally digitally signed) software installations and updates including packages and DMG files. Third-party frameworks including Sparkle are also available.

You can send your RAR feedback to Apple here: Product Feedback - Apple

"rar" files are not a native file format nor were they originally created By and Owned by Apple

To read more about who is accredited with creating this file format ( .rar )

Refer https://en.wikipedia.org/wiki/RAR_(file_format)

Why should Apple build rar/unrar into the operating system when there is a choice of free or fee apps in the Mac App Store. Look at the Unarchiver as a free example. There are others on that App Store panel.

If Apple added all the stuff that users wanted, the operating system would be in perpetual beta and Apple would again need to charge for it.

it’s annoying to download third party apps to “unrar”. This is a shame to suchh an experienced company.

But you only have to download such an app one. Takes a couple of seconds. problem solved permanently.