I think the main point of this lens is its speed - f/1.8 - and the fact that it is constant over the zoom range.
That means it would have to be looking through a wide piece of glass ALL the time (at max. aperture, that is).
And then it has to be retro-focus to project that wide-ish view into (even the APS-C) innards... So, size and weight.

As for its max. reproduction ratio - 1:4.3 - well, modest, but for the rest of what it can do I suppose it's OK.

I just hope it's price is "right".
Am.