The AUR targets Arch Linux only and I don't wanna run into the chance of there being a mismatch of packages I'm using and what other people r using. It makes it easier for me to ensure that, for example, the versions of the libraries I'm compiling against actually work. Like, if there is a library update in the arch repos that doesn't hit the cachyos repos by the time I do a build, it could have issues.
There is an arch x86-64-v3 repo, but I found it to be very far behind in terms of the most current packages, and I've experienced bugs with it.