There is a lot of abandonware and stuff where the companies just dissolved and ownership of any IP is questionable at best.
But also I don't think there's a way to give Nintendo/Game Freak money to play Gen 1 Pokemon at the moment? There's plenty of stuff like that. Sega and SquareEnix and some others have done a decent job of licensing/re-releasing some games. But there's plenty out there that they 'could' release and seemingly have no interest.