First: It's not a Unix system. It's a whole different tradition. For practical reasons it got "invaded" by the unix userland, though. But you already answered

First: It's not a Unix system. It's a whole different tradition. For practical reasons it got "invaded" by the unix userland, though. But you already answered it yourself. Legacy stuff. And because it is NOT a unix system porting the legacy stuff running on it would be even more difficult.