It’s also because the portability aspect of a Nintendo Handheld reaches 3 gaming markets responsible for 20m – 30m gamers per generation for Nintendo (realistically 25m each minimum).
The child gamer
The Japanese gamer
The Pokémon gamer
And this doesn’t diminish Nintendo at all, because they’ve done the work to own each of these segments. Nintendo could literally lose:
every non-Pokémon core fan (the die hard who bought Wii U: 20m)
every core-casual fan (those who pick Nintendo as a 2ndary / 3rd platform)
every casual fan (Wii type hype / fad gamers)
And still have a successful handheld, because those 3 main audiences (kids, JP, Pokemon) carry so much weight for their handheld platforms, that at worst they will produce 60m units sold, but realistically around 70m – 80m sells alone which is crazy.
Sony is close to having something like that, but the don’t quite have it as locked in as Nintendo does. Sony owns Europe just like Nintendo owns Japan. They don’t have that single IP to the level of Pokémon (instead they have a collection of IPs and the hope for continuous New IP). And they don’t have that single locked in community to the extent Nintendo has for kids/parents (they have their core and core-casual, but graphics and hardware play a role in keeping them especially that core-casual who only hear games are better on “X” platfrom). But regardless they do so well globally as a primary home console they too see huge global success.
Not to bring Xbox into this, but this is what they as a platform need to find their niche in. The most powerful console isn’t working for them. And why I’ve been saying since the latter half of the 360 era they need to move into the PConsole space and hopefully they learned so they can have their own successful niche.