It's also important to see university departments as groups of people who often will end up working together for decades, and therefore leadership will see internal politics everywhere. What does doubling your student body do to said politics? Better to minimize growth and keep people happy than deal with the risks of what happens when you end up with far more staff.

A lot of similar fun is occurring as the all the student body that isn't trust fund babies really wants to study topics that will pay well, which in many universities, might not even have a lot of political weight, or even their own dean. See all the universities where you can end up taking CS classes in 8 different unrelated departments, but where they really, really don't want to admit that 50%+ of the student body is programming, as building a proper umbrella for this, which then has so many students, takes a lot of power away from incumbents.