Interestingly this is actually a solved problem that we have forgotten the solution to. Copper naturally kills most pathogens. Brass door handles therefore act to prevent touch based spread of pathogens -- but plastic is cheaper.
I think it's not the price but the looks. Copper tends to oxidize and form an ugly green-ish hue of copper oxide, while proper plastics or other non-biocidic metal will not degrade in looks.
