Under what circumstances is it beneficial for an advisor to seek sole authorship when their advisees deserve to be listed as co-authors?
In my (admittedly naive) view, it would seem that the advisor would benefit more from co-authoring papers with their advisees than trying to pass the work off as their own, if nothing more than to show (to, e.g., tenure/promotion committees) that they are actively engaging their student researchers in the research activities of the group.


I tend to agree with your sentiment here. The problem is that not every evaluation committee (for tenure, for promotion, for regular end-of-the-year raises) is that sane.

Example 1: in my old university, we had for some time a hard tenure rule that required applicants to have a small number of recent single-authored papers. In applied computer science, basically nobody writes single-authored papers. It is simply not done. I don't know any concrete cases, but I would not be surprised if that rule led to some "single-authored" papers where the work was really done by a master student.

Example 2: I have heard of universities in Asia that base end-of-the-year raises on accepted papers. The concrete amount is dependent on the number of authors, as well as on the place in the author list, making it very attractive to "forget" authors or put the supervisor's name first.

Here on academics.SE, we tend to forget that academia varies more than we think, and just because a certain unethical behavior would not make sense in our university, there is no reason to believe that this is true everywhere.