There are two flaws to this logic, it assumes what you're suggesting is financially, and technologically viable.
With GTA5, I have no doubt it's possible to port it, but how much would Nintendo have to pay for the game? That's not how a platform holder should operate. Rockstar say, "give us thirty million dollars, and we'll give you a port", and Nintendo say yes?
First parties can't be paying for third party, multiplatform games, it sets a terrible precedent.
Also, going beyond PS360 games, technologically it becomes an issue, as well as financially.
It's not a case of what Nintendo wants, they can't just buy everyone.