Being that Arch is maintained with arch users in mind[0], building an installer for that user base would have to entail a wide range of option for unique use cases because that's whats expected of their users[1]. There isn't a "cop-out" or "plea" to users outside of the community because it was never a goal to appease them.
No, it wouldn't, because that versatility can be attained by... not using the installer, the exact same as the situation without an installer.
An installer, if anything, improves "user centrality" because you're making it more accessible and usable to most users with just the most common few options.
Not having an installer improves "dev centrality" (the few users who matter are the devs and other advanced users), over and against user centrality.
You could use the same thinking to argue against having a package manager. You might have to install a package manually anyway, so why bother providing packages at all?
At the end of the day, as others have probably already said in this thread, the maintainers are unpaid volunteers and choose to focus on certain things for their own reasons and using their finite resources.
There are other distributions that focus on other things and people can choose. If Arch chose to implement lots of convenience functions, that choice could be to the detriment of other strong aspects of the distribution.
An installer, if anything, improves "user centrality" because you're making it more accessible and usable to most users with just the most common few options.
Not having an installer improves "dev centrality" (the few users who matter are the devs and other advanced users), over and against user centrality.
You could use the same thinking to argue against having a package manager. You might have to install a package manually anyway, so why bother providing packages at all?