I reckon it would be a good idea, as other games have made it to the mobile which are on Playstion and Pc usually and being on the mobile would get more players interested. I think it may have to with thinking about the size and will the game be like the full console version or a simplified one and the costs would be huge to do as well. I hope when they do the games look good, and are made well so people can enjoy playing them and feeling like the console version.
I think they're avoiding that avenue because it would rob them of their handheld console money. They clearly still believed (given 3DS) that phones did not make handheld consoles obsolete. Maybe based on their declining sales & more people just using emulators they'll wise up & get exclusive with Apple.
Nintendo are going to be hugely successful in the mobile space, I'm sure of it. No other company even comes close to having so many awesome franchises. They've already announced that they will be moving in this direction but I guess they're taking their time to make sure everything is right. Unlike other mobile developers, Nintendo has a good sense of quality control and we can expect high quality games from them.