We don’t include pamac in the default install for several reasons but one of them is that pamac isn’t reliable outside of Manjaro. It is regularly broken on other Arch-based distros because it targets the Manjaro repos.
For more a more detailed response, please see here:
That being said, if you want to use pamac on your system, it is easy to install.
That is really out-of-date and over complicated. All that is needed is: