I would assume there is some licensing (perhaps cross licensing even) and patent issues that would prevent it from being entirely open sourced, particularly in regards to the GUI interface which Commodore was far from the first to implement. Amiga did GUI the best back in the day, but were far from the first to realize/implement the mouse/GUI concept.
Then there's the fact that any remaining IP holders or licensees are seemingly still hellbent on graverobbing the legacy of the platform as a whole, which is even more tragically sad. The original Commodore WB/OS would absolutely flourish even in this day and age if it was open sourced, it's still a stellar system.
