Why does nobody act like it is then? I don't use Arch but every Arch user talks about the Aur so matter-of-factly yet nobody treats it with the caution that it demands.

My sense of it is that as linux is gradually inching towards the general power user audience, there's a lot of "just use [distro]" or fashionable distros where they're all seen as flavors of one thing. In a sense that's true, but not in others like this. I'd also add the various atomic distros like Silverblue or derivatives which have other conditions you need to learn to work with. For AUR it seems to get recommended as a secondary way to get software, if it hasn't been brought into the original distros package repos then the next step is to just search AUR, make the shortest line to the goal and don't worry about the details.

As far as Arch goes, I wonder if Arch-based CachyOS is a factor as it's seen the high performance desktop linux.

They do? Arch exploded in popularity, but the forums were full of warnings.

My favorite Aur helper (pikaur) also asked you to check the PKGBUILD on every install or update, back when I used Arch.