Why are bronze and brass not as common metals to make things as they used to be in antiquity?

by Zoarob
Exostrike

we have harder metals to work that produce a better product in the end.

The main issue with bronze is that its a rather soft metal and doesn't keep its edge well. While early iron suffered similar issues (with less reparability) the moment you start getting cast and later wrought iron plus steel you have a might sharper metal that can be used in much more things.