Nintendo fans have had ports to choose from in the past but have declined. This generation has been different, and that's because Nintendo fans are buying these games, and they're buying them because they're getting solid ratings from reviewers and Digital Foundry. I'm not going to say that your reasoning is flawed, because it's obviously not and probably weighs the heaviest, but Nintendo fans don't gobble up every third party game just because it's "popular" or was the thing to buy last generation. They're picky and discerning and the developers are aware of this.
Portability/hybridability is a huge factor in why I buy many of the ports I have been buying. Especially since, unlike in previous generations of portable ports, we effectively lose zero gameplay quality in the transition. Yeah, sometimes we lose some visual quality, but the games are every bit as playable as their original versions, and THAT is why I believe we are getting so many old ports - there's ALWAYS been a market for portable versions, but now we can finally get those AND keep the quality! Plus it's nice to be able to plug it into the TV so effortlessly and still have the classic console experience.