I was going to object but you are absolutely right. Most Linux installs are instances of something that are created and destroyed without a human ever touching them. However, I wouldn't go so far as to characterize these features as technical debt. A fully functional Linux system should be able to tell users if they have mail, for instance.
I'm not just talking about containers or managed servers, though. Most Linux desktop systems rarely or never have a user perform a PAM login in a situation where the mail message would be seen. (Opening a terminal emulator doesn't go through PAM; it starts the shell directly, and logging into X / Wayland might use PAM, but doesn't display login messages.) And, of course, it isn't relevant at all on embedded systems; a lot of those probably aren't even running a getty.
> A fully functional Linux system should be able to tell users if they have mail, for instance.
Hot take: storing and processing email shouldn't be a required function of the OS. It should be an optional feature, just like serving web pages over HTTP or having a graphical desktop.