I don't think it makes sense to use it on even small laptops screen to be honest so I don't really see the point. You'd have to redo the UI and whole paradigm entirely anyways for it to be meaningful on small devices. But there is certainly not any obstacle to porting - from my own experience with ossia & Qt, it is fairly easy to make iOS and Android builds, the difficulty is in finding a proper iOS and Android UX.
In particular C++ code works on every machine that can drive a screen without too much trouble - if the app is built in C++ you can at least make the code run on the device... just have to make something pretty out of it afterwards.
The point is that the parent poster mentioned tablets and phones which you don't address in your point. Of course your examples aren't written 6 times, but they support fewer platforms too (only desktop).
Off-topic, but regarding Bitwig: of course it makes perfect sense to use it on smaller devices. Not phones, but tablets. It's even officially supported with a specific display profile in your user interface settings (obvious target amongst others: windows surface). This is particularly useful for musicians on stage.
