I understand that a scientific term need not be constrained by its etymology. But is there some significant reason why astronomers choose to call all elements heavier than helium "metals"?
Are metals (in the chemist's sense) commonly easier to detect by spectroscopy than non-metals? Or, were they easier to detect a hundred years ago? Do they typically have more diagnostic value or a more crucial role in stellar evolution? I know Iron specifically has a key role. They are very much less common by weight in the universe, unless you include Carbon as a metalloid, but of course they are much more numerous in the periodic table than non-metals.