I dont think theres really anything wrong with having metal armor. Ive never seen it person, but I know makers have made them from either aluminum or I think 18 guage steel, that I may be wrong about. Other things is that they may sometimes sacrifice details, for the materials its made of. Dont get me wrong, Ive seen some great looking armor made from metal, such as wickedbeard's Jango armor. Another thing may be weight, but that goes back to what metal and what thickness the armor is. I personally wouldnt mind haveing a set of metal armor, it makes it that much more realistic in my opinion.
-tubachris