I commented on his page about the possible causes of the over-enrollment/under-sized political science department: pre-law is a factor; it is a relatively easy major (no or little math); good for folks wanting to go into government; and universities don't seem to mind huge poli sci classes (unlike English lit which needs smaller seminars/classes).
Poli sci and department sizes
Via Henry Farrell and Chris Blattman, an article showing consistent disparities across disciplines in student-faculty rations (technically majors-faculty ratios), with poli sci consistently turning up as an extreme case of too few faculty for too many students, followed by econ and psych. As Blattman puts it, this has direct bearings on "why your economics and politics professors seem to have so little time for you."
McGill is typical in this regard, having the worst major/student ration to professor. Part of the reality here, and I say this with all due modesty, but our profs get signficantly better than average teaching evals. So, one of the reasons our classes are really large is that we do a good job of lecturing. Another is that McGill students (like Oberlin students) are passionately interested about the political world around them, so they take our classes and are quite engaged in them. Which, in turn, makes the classes more enjoyable for the students and the profs.
As a result, I teach an intro to International Relations class each fall to 600 students or so. And the other intro classes are in the same ballpark. Is this a good way to deliver the content? Depends on what you think about lectures, because there is really not that much of a difference between 100 students and 600 except more teaching assistants.