Convenience and confidentiality, e.g. you don't want to print grant proposals or recommendation letters on shared printers.

A common setup is to have shared printers for high volume things like exams and additionally have low volume printers per group.

> 30 printers all different

Have you tried endorsing certain models? Most researchers don't want to spend time picking out printers and will just get a random one. If you suggest one, they will probably just agree.