The number of citizens is the number of tasks that can be performed simultaneously in the game; number of citizens required to complete a task = difficulty of the task. In real life, it is impossible for one person, for example, to both study and build at the same time - in the game everything is exactly the same.
If you focus only on resources - there are no special problems with resources in the game at all - there is even a problem that there is nowhere to invest them, because, again, all the citizens are busy.
In other words, if the University does not require citizens, it will devalue the learning process at the University. The Library doesn't require citizens, so why turn the University into a clone of the Library?