Comment by iterance

In coursework, references are often a way of demonstrating the reading one did on a topic before committing to a course of argumentation. They also contextualize what exactly the student's thinking is in dialogue with, since general familiarity with a topic can't be assumed in introductory coursework. Citation minimums are usually imposed as a means of encouraging a student to read more about a topic before synthesizing their thoughts, and as a means of demonstrating that work to a professor. While there may have been administrative reasons for the citation minimum, the concept behind them is not unfounded, though they are probably not the most effective way of achieving that goal.

While similar, the function is fundamentally different from citations appearing in research. However, even professionally, it is well beyond rare for a philosophical work, even for professional philosophers, to be written truly ex nihilo as you seem to be suggesting. Citation is an essential component of research dialogue and cannot be elided.