Virtual console sales. Nintendo doesn't want you to play those titles on a tiny touch screen. I agree with them there; screen + tactile buttons are a much superior way to play.

The heart of it all is in the virtual console emulator though. If you want to play Super Mario World, Metroid, Earthbound, and other classic titles, they want you to go through their store on their systems where they have total control. The DS family and Switch are both portable systems, so to them, there isn't much incentive to make sure Android/iOS emulation are bug free.

There is also that stigma attached to paying for mobile games. I mean, Super Mario Run did really well, and it is a polished runner that (in my opinion) is worth the full price tag. But the prevailing logic is still that paid games are for consoles/Steam and free games are mobile fodder.

Nintendo likes to keep it's IP on it's own hardware, but Square Enix (for one) has released several of it's most famous RPGs on Android (most of the Final Fantasies, Chrono Trigger, etc.).

Updates do have to be made to support a touch interface, which is why I think you're request is not a trivial undertaking for most companies. RPGs work, but I can't imagine playing a game like Contra on a touch screen.

Cause without buttons they suck :)

This is the real answer. Nintendo don't want to sell $1 games, because that would re-anchor Nintendo customers to lower price-point expectations, in contrast to the $5/$15/$30/$70 pricing tiers they have right now. But Nintendo just don't (or rather, didn't, until Super Mario Run) have the in-house experience working with mobile form-factors to produce even original games that would stand out enough from the dreck on the app store to be "worth" more than $1 to consumers. So they just didn't bother with mobile.

They could design a classic bluetooth controller and sell it for cheap. I'm using the expensive, but awesome Switch Pro Controller on my Android's SNES emulator.

People have their phones with them in a lot of cases where they just can't or won't bring any accessories: at a nightclub, in the toilet, etc. If this is the majority of time when you'd want to kill time on your phone, controller-requiring games would be pointless for you.

Mind you, if you can force people to bring the accessory wherever they bring the phone, the calculus shifts. The Switch essentially is a Pro Controller duct-taped to an Android tablet; and it's a lot easier to convince people to buy one. :)

Yeah accessories are a challenge. But your comment made me think - how about a phone case that doubles as a controller? Kind of like the Surface keyboard as a phone case or protector with tactile buttons? I found a hard case called Flitchio but not sure if it made it to market and I don't like the joystick design [1]. Here's one closer to what I was thinking [2].

[1] http://www.pocket-lint.com/news/134420-consoles-beware-flitc...

[2] http://portabletech.co/

Because Super Mario Bros would be an absolutely terrible experience on a touchscreen. The game is hard enough on the original console with a zero-latency CRT. Put it through an emulator and a bunch of layers of abstraction to a comparatively glacial LCD, then try to control it with non-tactile onscreen buttons? No, thank you.

Why doesn't Nintendo write new games for smartphones? (Ignoring the odd exception.)

Same answer really. They make games consoles.

Licensing

Because it would reduce demand for them if they were to try to get them onto the Switch with a much higher markup.

It might, but they've only shipped about 1M Switch units, which is a rounding error compared to the ~2B smartphones in use. If Nintendo really doesn't want to port/emulate because they want to prop up their hardware sales (or because they dislike touchscreen-only controls), they're acting very much against their best interests.