Because in due course we'll have Unity across all of these form factors. For now, however, Android is better on the phone UI than Unity, and so we're making it possible for people to start converging on the phone today with Android rather than waiting months for the Ubuntu phone UI itself.
You speak in the first person, are you involved with this project ?
"The hottest places in Hell are reserved for those who, in times of moral crisis, preserved their neutrality." -- Dante