Because most jobs and projects have complex requirements that aren't satisfied by the standard library of ANY language. But that's irrelevant for teaching. The

Because most jobs and projects have complex requirements that aren't satisfied by the standard library of ANY language. But that's irrelevant for teaching. The Java/.NET stdlibs are huge. They are more than sufficient to teach basically any of the foundational skills. Then if you want to learn Hibernate or ORMs, no problem, that's only a small extra step.