Since I obtained closing priviledges and can thus use custom close reasons, I find myself typing the following sentence on a daily basis (and before, I flagged questions to which this would have applied regularly):
This question appears to be off-topic because it is about the content of an academic discipline and not about academia itself.
It thus seems to be useful to me to have a predefined close reason for such cases which then can also be used to give the askers some help at hand where to ask their question (if at all).