What do you mean you would have to learn an entire new alphabet? The alphabet is the same Latin alphabet used every day by English speakers and does not even include any diacritics or extra letters. It couldn't be easier. Again, that's one reason for the usefulness of this romanization system: you can type it in any situation you'd type normal English text.
It's all well and good to expect people to just "learn 한글", but people learn at different paces, a fact that I'm well acquainted with after five years of teaching English. For those who haven't mastered 한글 yet and still need to type Korean text, keyboard romanization is a viable alternative.