It is a different situation, because Nix packages are part of the Nix distributdis, while AUR packages are not part of Arch. AUR packages are more like Ubuntu ppa's, you can add and run them, but you are on your own risk.

Also,it is a huge number of packages (about 114,000) which are many used by relatively few people. Each arch user has in average probably only a few of these.

So, it makes sense that users review them by themselves. If you can't do that, you should probably not use them.

average user

It is Archlinux' mission statement that its average user knows how to do such things. The installation process is based on handling PKGBUILDS. AUR helpers are explicitely unsupported.

The onus here is on Arch-based distros that decide this vast collection of build scripts equals a software repo, is a good "selling" point, and decide to integrate it into the distro or even the package management.

All that said, the AUR is not the only user repo that is plagued. These sort of malware attacks need to be addressed somehow.

Somehow I really doubt telling an average user to assessing pkgbuild on their own

Arch Linux is not really made for the average user, and using code from AUR even less so. I doubt it that everyone using Arch+AUR or CachyOS or youname it is served well by this.

And making it kind of accepted norm to run untrusted code as a non-technical user will bite the Arch community in the ass. For Arch, it is a phony measure of success to have many such users.

This is also a result of Windows user attitudes leaking into the Linux universe. You need to discern code and data, and you can't run untrusted code, period.