alt Hacker NewsWindows tried this for a long time and literally no app was able to make it work properly. I spent years of my life making Excel have a sane rendering model that worked on device independent pixels and all that, but its just really hard for people not to think in raw pixels.
And yet every Android app does it just fine :)
The real answer is just it's hard to bolt this on later, the UI toolkit needs to support it from the start