One important reason was that ARexx's compound variables enabled menu hierarchies to be defined directly from rough sketches of what was required. In addition to this ARexx has very powerful string handling functions (even better than Basic) so I was virtually able to write the code whilst I thought about what was needed.
I woudn't dream of knocking the pc in general, but nevertheless it must be said that to prototype this particular application using Basic, C++, or any language commonly available to pc users would have taken a lot more time!