When NS user base will be large enough, more games could start being developed with NS as entry-level HW, but for existing games that were developed on more powerful platform, a port, if possible, will happen only if the predicted sales will be large enough to justify the costs. In some cases NS HW specs aren't an obstacle, but, as others wrote, if the game didn't age well, or if potential buyers are too few, a port won't happen, unless Ninty pays for it.
A possible solution to make some ports happen could be crowdfunding, it could also be a way to see if NS gamers really want those games.