I asked this question from my professors one of them told me that for DC supply we need pure copper transmission line which is very expensive, other told me that the transmission line fact isn't important that much the only reason that we can't use DC that it can't be step up or step Down. I was thinking that as DC has negligible losses as compared to AC but the only disadvantage is that we can't step up or step down it so why don't we produce the desired voltage and current in power station and supply it to for home or industry???