The most useful university courses and degrees are the hardest to get into. For example, most people would benefit from knowing something about accounting. But do universities facilitate the study of accounting? No. Everywhere admission into Bachelor of Commerce and Bachelor of Business Administration programs is restricted.
It's the interests of business schools to turn away customers. As faculty complements respond only slowly to changes in student numbers, in the short run fewer students mean smaller classes and a generally pleasant life for faculty. Moreover, when admission to business school is difficult and competitive, only the best students are able to gain admission. Hence a Bachelor of Commerce degree becomes a signal of ability - specifically, the ability to earn high school grades above the entrance cut-off.
Yet if competitive entry requirements mean that Bachelor of Commerce graduates are, on average, better students than other graduates, they will also be better employees (providing success in school and success in the workplace is correlated). So employers, regardless of whether or not business schools actually teach anything useful, will prefer to hire B Comms. Potential students, observing this, will try even harder to get into business school - and so the cycle continues, until the business school has a shiny new building and every professor earns over $200,000 a year.
I've picked on business here, but a similar story can be told for many other degrees. Another factor leading to admission restrictions is that many useful courses, for example, ones involving writing, tutoring, or hands on data analysis, require a lot of instructional resources. It's cheap to pack students into a 500-person lecture theatre and give multiple choice exams.
What can people in the arts and social sciences do to keep up student numbers, and at the same time protect the reputation of their programs?