I imagine one reason why fit artwork to artboard isn't and option is because strokes applied to an element don't scale with size. So for example, a 10pt stroke is still 10pt even if the element it's applied to is scaled down by 50%.
One solution would be to select all (cmd a) then Object > Path > Outline Stroke. then group everything (cmd g) and resize whilst holding shift to proportionately scale up or down. The problem you will have with this is that the action of outlining strokes stops them being editable as a normal stroke.