This is a very good observation. The 'login' infrastructure deals with authorization to run processes on the computer, which is orthogonal to managing characteristics of individual processes, such as whether they areĀ transient or persistent. Admitedly, the logout process has to deal with the lingering processes: Windows, for instance, throws a dialog box asking to terminate the apps. This is somehow a violation of layering which I just pointed out above, but I think it is correct in asking for user intent.
It seems to me that what's happening is that systemd is now enforcing this "login session" perspective... metaphorically speaking, gluing the transparent overlay onto the map (but don't worry! they also provide a special adhesive remover!). This makes it that much harder for people to make use of what's underneath without viewing it through the overlay... which, as it turns out, is a *very* common thing to do (screen, tmux, nohup, etc.).