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?

[DaRev]

Troll_Whisperer said:
IPs that are more popular among a more casual, less informed audience have better legs (e.g.: Gran Turismo).

Most Nintendo's IPs are like these, with some exceptions like Zelda, that have more core followers that know when the game is releasing, want to play it asap, etc.

This ^^, but I'm not sure GT is the best example here, as being a game that appeals to casuals.