So it's widely known as a fact that many Nintendo games have ridiculous legs. But here's the question that no one really bother to ask...why is this so?

[Mummelmann]

chapset said:

Mummelmann said:
Timeless gameplay that doesn't live off of trends and current gimmicks as a main sales incentive. That's also the reason why Gran Turismo has such great legs and games like Baldur's Gate can be re-released and still do well.

not completely true after the wii and wii U, they popularise the motion gaming gimmick with the wii and they tried to get easy money with the tablet gaming craze with the wii U, but they do have games that don't follow trends with mario and pokemon

Wii Sports, Wii Play and Nintendoland belong to this category of gimmick driven games. Besides those, most Nintendo titles didn't really make heavy use of the Wii-motes capability at all, mostly waggle and some games were even best played with a classic controller (Mario Kart, NSMB, SSBB and Zelda, for instance).

The Gamepad as a gimmick to drive sales isn't working and won't work, the concept is entirely too weak and aimed completely wrong, Nintendo are being handily beaten on the touchscreen control by tablets and smartphones. The Gamepad was a horrible idea to begin with and the hardware and software sales confirm as much.

The Wii-mote rose quickly and was a really big hit, this was one of the keys but the main reason why Zelda, Mario Galaxy, NSMB and Mario Kart have such amazing legs and attach rates is simply due to the aforementioned timeless gameplay and reliance upon a solid core, playable structure rather than gimmicks and effects. As mentioned, the Gamepad will do nothing good for Nintendo, it might end up harming them in the end. If they make their games with the same philosophy as ever though, we should see some great legs for their main franchises in the 8th gen as well.