They exist as collection of scripts to install precompiled (or to be compiled) packages, maintained by 3rd party developers as means of convenience, they’re not to be blindly installed as system packages (which I agree is what often people would do)
It offers certain autonomy to users on top of stable system to build/preinstall packages when they deem it necessary.
It’s always advised to check what’s happening with AUR scripts & updates, in archwiki with well noted warnings.
These things don’t sit well with script kiddie style of doing things!
These things don’t sit well with script kiddie style of doing things!