According to this very nice graph reported by Chris Blattman (original article here ), the answer may be ‘more people than there are realistic levels of faculty to teach them.’ There is some variance, but average student-faculty ratios for political science are considerably higher than for economics and and much, much higher than for most other degrees on campus. In the authors’ words:
[In University of Virginia, t]hree social science disciplines – economics, psychology, and politics – have more than 20 majors per tenure-track faculty member. Even expanding the definition of faculty to include non-tenure-track faculty (which in the case of economics are mostly graduate students teaching independently), the ratios are still in double digits. At the other end of the distribution, we find a collection of physical sciences (notably physics and astronomy) and languages such as German and Slavic where majors per faculty are fewer than five. This variation in ratios of majors to faculty observed at the University of Virginia is not unusual; similar metrics from other colleges and universities suggest strong parallels.
The authors’ explanation:
we suspect that differences across fields in the allocation of faculty relative to student demand persist even after accounting for relative salary, research preeminence, and pedagogical differences. This residual disparity might be the product of political forces within institutions that favor certain disciplines. For example, some of the disparities observed across fields as well as the stickiness of the adjustment process may well reflect a political process within the university favoring incumbency, as tenured faculty in low-demand departments create barriers to adjustment through time-intensive protest or efforts to increase student course demand artificially through curricular requirements and other incentives.
I’m actually not at all opposed to disparate resources going to departments with few majors (academia should have multiple redundancies), but as the authors politely suggest, there is little doubt that these disparities are at least as much the result of internal factional politics as any coordinated process of decision making.