Game fans often times have no concept of reality.
It's easy to sit behind a keyboard and say do this or that with no financial risk involved. When it's your own small company and you have to run a business that puts food on people's tables ... then you can't just magically support every platform, you have to narrow things down to where you feel you will get the most money.
A lot of these Nintendo fans that beg for ports would probably sing a very, very different tune if it was their life savings invested into a company and every project had to make a profit or you'd have to start laying people off or even close up shop.
And no, Nintendo is not responsible for marketing every third party game per se, but they are responsible for the overall direction/demographic appeal of their consoles, and they are the ones making a console aimed at a audience that doesn't give a crap about consoles to begin with -- kids and casuals.
In that ecosystem a third party making a game like Need For Speed isn't going to be successful because there's no audience for that type of game, they all go elsewhere, which IS Nintendo's fault for not creating a well rounded platform that appeals to a wide variety of demographics (not just a short sighted view of the market where they can sell Mario games and desperately try to bring back the Wii Fit crowd).
They have all the resources in the world to make a console that can appeal to a wider range of gamers and not ostracize or alienate core gamers so much, but they purposely chose not to go that route and that consumer has an easy choice of simply ignoring Nintendo.
