I mean, if someone said, "I've successfully ported Vim to Android!", my first thought would be, "Why in god's name would I want to run vim on my phone?"*
* Ruling out, of course, someone plugging their phone into external KVM.
If you think about it, no one knows the user's use case better than they themselves do. So who is in a better position to determine what functionality is most important to have on their tiny phone screen? Which components need to be bigger and more prominent or smaller and less prominent according to their workflow? Etc.
In other words, the GUI isn't optimized for anything by the developer, but the user can make it optimal for themselves.
The first class of application probably won't run in to any issues with just designing for a smartphone UI and not bothering with anything else.