As for reducing: research, grad programs, journals, media inquiries - these are not optional for profs
You are accustomed to professional managerial class luxuries that are unavailable to most hard working folks
Some of whom might have good options for changing jobs, or good hopes of things improving in the near future, but for many it would be the lesser evil compared to trying to find a different job with the same positives (whether salary or other motivation) but without those negatives.
For a tenured professor (and someone who runs the department's grad program and teaches many classes almost certainly has a tenure) all of those are optional. During my PhD I have seen all sorts of arrangements, including tenured profs who taught minimum load and did nothing else. No grad students, no special courses, no seminars, nada. I am not advocating this. It is, in my book, not a good approach unless you spending all other time to solve Riemannian Hypothesis or something like this. But tenure gives a prof a lot of leeway on how much to work and what to work on. My 2c.
When I said that a particular job task is not optional I mean that not doing this task will lead to a disciplinary action from the employer (being fired, put on a performance improvement clock with the HR, etc.). Reducing those tasks brings in one set of considerations.
Your definition of "obliged", if I understand it correctly, is primarily a self-assigned or a community-expected one: "if I stop running this seminar or remove myself from that editorial board, I will feel I am not doing all I can / my colleagues will look at me askance". But it will not trigger retaliation from the employer. Reducing overload from those tasks brings a completely different set of considerations.