One reason could have to do with very strict sense of quality. If the games would run on wide variety of platforms, Nintendo couldn't make sure that the experie

One reason could have to do with very strict sense of quality. If the games would run on wide variety of platforms, Nintendo couldn't make sure that the experience for user is exactly what they want it to be, unlike when games are played in their own specific emulation hardware and gamepads. I think a Mario game played without guaranteed tight controls could hurt the expectation what Mario games are.