I want to ask what does a dev needs to add a program to be installable with pacman, not only with the AUR.
Become a trusted Arch Linux package maintainer, and make sure you have a lot of time (and hair) to spare. (Or convince a Trusted User to adopt your package.)
It needs to receive enough votes, regardless, and adhere to certain policies about being in the official repositories. (To be “promoted” from AUR to Community repository.)
(Think of how Apple has “standards” for its iOS App Store.)
EDIT: The reverse is also true, and there are several examples in the past where a package in the Community repository is demoted (or dropped) into the AUR because the Trusted User no longer wishes to maintain it and/or other technical reasons.
As far as the Manjaro community repo is concerned, please see: