It’s false to say that Nintendo is the only company that has cooperative ownership of games, this seems to be common practice.
It depends on the copyright laws. Keep in mind, trademarks and copyrights are different things.
For example, some company called “Natsume” owned the trademark for Harvest Moon, but the copyrights are owned by Marvelous, so Marvelous is able to release old Harvest Moon games under the name “Story of Seasons” through their own localization firm XSeed. But Natsume has no rights to the game, even though they own its name.
But copyrights for videogames are a little more complex since there are multiple elements with different rules, and they are not necessarily seen as one entity. There’s music, art, code, and written story.
Additionally, laws across international borders (especially those not in the TPP) have some major hurdles if they are developed between multiple countries. GE007 is basically impossible to port due to many companies holding a stake in the game and having differing agendas.
There’s also the matter of old laws applying to certain properties. So even if things are updated, that doesn’t retroactively apply. Additionally, contracts of ownership may apply. Perhaps companies (such as Nintendo) maintains an old custom due to tradition.
I am not sure all the rules for Japan (or any, really), but I’d say that’s probably the reason why Japanese companies co-own copyrights for videogames.
I describe myself as a little dose of toxic masculinity.
